Being underwhelmed by the priest at first glance I was playing with some builds for a melee plate wielding priest when I realized I could run a cha 10 priest and it would hardly matter to me.
The fact is very few priest powers use CHA at all and for those that do, it ussually makes only the slightest difference if your cha is 18 or if your cha is 10
Analysis of Cha related powers
Channel Divinity - Turn Undead
This power damages undead and pushes them 3+ cha modifier squares and immobilizes them.
This power is probably the most powerful in regards to what your charisma is 3 squares vs 7 is certinaly enouph to move mobs out of charge ranges however as a melee priest you may not even want that since they will be immobilized anyways and now you might not be able to engage them in melee combat.
Im not 100% clear on the push rules but if you could choose to not use the full push it would make this power more usefull and cha more useful but this is as good as it gets.
Sacred Flame - At will power
This is the only at will power that uses charisma. After this attack hits an ally within 5 squares can do one of the following things.
1) Make a saving throw
2) Gain temp hit points = Cha mod + 1/2 your level
This first effect is nice and lets you get rid of ongoing damage or other effects while the second at low levels is very nice. The higher level you are the less this matters both because monsters hit hard, your level bonus is going to exceed your cha bonus and your cha bonus isn't going to fluctuate all that much. A nice power but suffers from diminishing returns on the cha portion and with 3 other at wills, you don't have to take it.
Cause Fear - Encounter - Cleric Attack 1
Causes the creature to run away from you at its full speed + your cha modifier provoking opportunity attacks as it flees.
So basically you can get some extra squares on the target fleeing.
Command - Encounter - Cleric Attack 3
This dazes the target and lets you either
1) Knock the target prone
or
2) Slide the target 3+ cha modifier in squares
So on effect where cha doesn't matter and a 2nd where you can move him further (a common cha theme)
Consecrated Ground - Daily - Cleric Attack 5
This is the heaviest cha using power. Its a burst 1 (in latter tuns you can move the origin of the burst up to 3 squares). Enemies in the burst take 1d6 + cha mod dmg. Allies Heal 1 + cha mod (which will become another cha theme) You can also sustain this power with a minor action.
Bastion of Health - Encounter - Cleric Utility 6
Target can spend a healing surge and you can add your cha mod to the heal. So once per encounter somebody gets 4pts of extra healing at 6th level.
Break the Spirit - Encounter - Cleric Attack 7
Does radiant damage and till the end of your next turn the target suffers - your cha modifier to its attacks. -4 to hit is nothing to scoff at it 4E to bad its only for 1 round.
Strengthen the Faithful - Encounter - Cleric attack 7
One of the only powers that uses a melee weapon and where cha matters although not that much. Does damage allows an ally to use a healing surge and adds your cha mod to whatever the surge heals. 4pts is even less impressive at 7th level that it was at 6th.
Mass Cure light wounds - Daily - Cleric Utility 10
All allies it the impressive burst 5 regain hps as if they spent a healing surge. Add your cha modifier to the hps regained. 4pts at 10th level now.
Inspiring Strike - Encounter - Cleric attack 13
does damage and your ally gains 15hps + your cha modifier. The bulk of the points you regain is still fixed.
Plague of Doom - Encounter - Cleric attack 13
Does a bunch of damage and enemy takes a penalty to his defense = to your cha modifier till the end of your next turn. Decent use of cha here.
Purifying Fire - Daily - Cleric Attack 15
Do damage and do ongoing damage and all allies in the burst 2 regain 5 + your cha modifier hps.
Thunderous Word - Encounter - Cleric attack 17
Does damage and you push the target 3+ your cha modifier. Same effect as turn undead except you can use it on any enemy in the close blast 5.
Healing Torch - Encounter - Cleric Attack 23
does damage and allies in the burst gain an AC bonus = to your cha mod and can spend a healing surge and get extra hps = to your cha mod.
Decent Cha power
Sacrificial Healing - Encounter - Cleric attack 27
Does damage and everyone in within 10 squares can spend a healing surge and adds your cha mod to their hps gained.
Sunburst - Encounter - Cleric attack 27
Does some damage and allies in the burst gain 10 + cha mod in healing.
Summary and impressions
Damage - In only one power is charisma used for damage calculations.
Healing - Used often in healing but the effects are very normally 1pt of extra healing per point of charisma so it suffers greatly from diminishing returns as players hps rise as well as monster damage. The absolute best use is the at will power which gives temp hps, which could equate to your cha in healing every singe round.
Control There is a small subset of powers that let you push targets and it is X number + cha mod good for ranged priests, less useful for melee
Other There is one power that gives an AC penalty for one round equal to your cha and one that gives bonus to hit for 1 round based on your cha. This is very nice for a high cha priest but the number of powers that use this is tiny.
Addendum
Before I get yelled at I'm not saying cha is useless for priests its just not that big of a deal (especially compared to 3.5). As a priest that focus's on melee you could have an 8 in wis and never care one way or the other. You could even make a ranged priest and it wouldn't have that big of an effect if you didn't want it to.
Certainly there are some priest builds that you'll want to have high cha (anyone who wants to be an angelic avenger) but you could also take those extra points and use them to qualify for better armor feats or feats that let you do more radiant damage.
The fact is very few priest powers use CHA at all and for those that do, it ussually makes only the slightest difference if your cha is 18 or if your cha is 10
Analysis of Cha related powers
Channel Divinity - Turn Undead
This power damages undead and pushes them 3+ cha modifier squares and immobilizes them.
This power is probably the most powerful in regards to what your charisma is 3 squares vs 7 is certinaly enouph to move mobs out of charge ranges however as a melee priest you may not even want that since they will be immobilized anyways and now you might not be able to engage them in melee combat.
Im not 100% clear on the push rules but if you could choose to not use the full push it would make this power more usefull and cha more useful but this is as good as it gets.
Sacred Flame - At will power
This is the only at will power that uses charisma. After this attack hits an ally within 5 squares can do one of the following things.
1) Make a saving throw
2) Gain temp hit points = Cha mod + 1/2 your level
This first effect is nice and lets you get rid of ongoing damage or other effects while the second at low levels is very nice. The higher level you are the less this matters both because monsters hit hard, your level bonus is going to exceed your cha bonus and your cha bonus isn't going to fluctuate all that much. A nice power but suffers from diminishing returns on the cha portion and with 3 other at wills, you don't have to take it.
Cause Fear - Encounter - Cleric Attack 1
Causes the creature to run away from you at its full speed + your cha modifier provoking opportunity attacks as it flees.
So basically you can get some extra squares on the target fleeing.
Command - Encounter - Cleric Attack 3
This dazes the target and lets you either
1) Knock the target prone
or
2) Slide the target 3+ cha modifier in squares
So on effect where cha doesn't matter and a 2nd where you can move him further (a common cha theme)
Consecrated Ground - Daily - Cleric Attack 5
This is the heaviest cha using power. Its a burst 1 (in latter tuns you can move the origin of the burst up to 3 squares). Enemies in the burst take 1d6 + cha mod dmg. Allies Heal 1 + cha mod (which will become another cha theme) You can also sustain this power with a minor action.
Bastion of Health - Encounter - Cleric Utility 6
Target can spend a healing surge and you can add your cha mod to the heal. So once per encounter somebody gets 4pts of extra healing at 6th level.
Break the Spirit - Encounter - Cleric Attack 7
Does radiant damage and till the end of your next turn the target suffers - your cha modifier to its attacks. -4 to hit is nothing to scoff at it 4E to bad its only for 1 round.
Strengthen the Faithful - Encounter - Cleric attack 7
One of the only powers that uses a melee weapon and where cha matters although not that much. Does damage allows an ally to use a healing surge and adds your cha mod to whatever the surge heals. 4pts is even less impressive at 7th level that it was at 6th.
Mass Cure light wounds - Daily - Cleric Utility 10
All allies it the impressive burst 5 regain hps as if they spent a healing surge. Add your cha modifier to the hps regained. 4pts at 10th level now.
Inspiring Strike - Encounter - Cleric attack 13
does damage and your ally gains 15hps + your cha modifier. The bulk of the points you regain is still fixed.
Plague of Doom - Encounter - Cleric attack 13
Does a bunch of damage and enemy takes a penalty to his defense = to your cha modifier till the end of your next turn. Decent use of cha here.
Purifying Fire - Daily - Cleric Attack 15
Do damage and do ongoing damage and all allies in the burst 2 regain 5 + your cha modifier hps.
Thunderous Word - Encounter - Cleric attack 17
Does damage and you push the target 3+ your cha modifier. Same effect as turn undead except you can use it on any enemy in the close blast 5.
Healing Torch - Encounter - Cleric Attack 23
does damage and allies in the burst gain an AC bonus = to your cha mod and can spend a healing surge and get extra hps = to your cha mod.
Decent Cha power
Sacrificial Healing - Encounter - Cleric attack 27
Does damage and everyone in within 10 squares can spend a healing surge and adds your cha mod to their hps gained.
Sunburst - Encounter - Cleric attack 27
Does some damage and allies in the burst gain 10 + cha mod in healing.
Summary and impressions
Damage - In only one power is charisma used for damage calculations.
Healing - Used often in healing but the effects are very normally 1pt of extra healing per point of charisma so it suffers greatly from diminishing returns as players hps rise as well as monster damage. The absolute best use is the at will power which gives temp hps, which could equate to your cha in healing every singe round.
Control There is a small subset of powers that let you push targets and it is X number + cha mod good for ranged priests, less useful for melee
Other There is one power that gives an AC penalty for one round equal to your cha and one that gives bonus to hit for 1 round based on your cha. This is very nice for a high cha priest but the number of powers that use this is tiny.
Addendum
Before I get yelled at I'm not saying cha is useless for priests its just not that big of a deal (especially compared to 3.5). As a priest that focus's on melee you could have an 8 in wis and never care one way or the other. You could even make a ranged priest and it wouldn't have that big of an effect if you didn't want it to.
Certainly there are some priest builds that you'll want to have high cha (anyone who wants to be an angelic avenger) but you could also take those extra points and use them to qualify for better armor feats or feats that let you do more radiant damage.
