I pose this quandary . . . . .

[Salthorae]

Sounds right to me, if you did 50/50 damage it would be +1 DC as it would be Evocation [Acid, Fire] if you do full acid damage your spell is Evocation [Acid] and so deals no fire damage and so the feat doesn't apply.

 

[Squire James]

Seconded... converting all the damage to acid makes it an acid spell rather than a fire spell. At least, that's how I would rule it. Some enterprising rules lawyers might note that the feat description says nothing about changing the descriptors of the spell, but I tend to cast Harm and Quickened Inflict Critical Wounds on such fools!

Of course, the drawback of the 50-50 option is that it makes the spell weaker against enemies with either resistance, and even more so against those who resist both! On the other hand, it also means it will do SOME damage if they are resistant/immune to one of them, so a fire/acid combo is a good thing to try to kill a troll with, for instance.

 

[Empirate]

So long as stuff like Signature Spell is allowed, you might want to take a look into Bloodline of Fire, another FR specific 3.5 feat (in Player's Guide to Faerûn). This little feat grants +2 to caster level with ALL [Fire] spells. Stackable with other CL increasers, btw. Also, look into Spellcasting Thematics (same source), which allows you to pick one spell at each spell level and increase its caster level by +1.

Makes for a nice combo for my own blaster Wizard in a PF campaign that allows some 3.5 stuff. CL increases is really where it's at to keep blasting viable at low to mid levels.

 

[Scott DeWar]

actually, it isa pathfinder feat!

from the D 20 pathfinder srd (Spell Specialization - Pathfinder_OGC) :

Benefit: Select one spell of a school for which you have taken the Spell Focus feat. Treat your caster level as being two higher for all level-variable effects of the spell.

This character that i am researching this for is in living pathfinder - no 3.5 stuff accepted. thanks for the idea though.

Makes for a nice combo for my own blaster Wizard in a PF campaign that allows some 3.5 stuff. CL increases is really where it's at to keep blasting viable at low to mid levels.

that is pretty much where i am headed. "Greater Spell Specialization" is another goal for me.