One of the main advantages of the original suggestion is that it does not require a table. I'd like to keep it that way, which is why I don't like the "Cha check" approach.
How can a character get a +6 to Cha in one level? The only way he can do that is through heavy use of magic items.
That said, I agree that getting a +X to cha count as getting a +2X at turning might be excessive.
How about instead setting DC=1d20+Cleric level+1/2 Cha bonus (or 5+... or something)? Not clean, but at least no table...
The undead would then be turned if they fail the Will save (or 10+Will if the DM is lasy...). They would be destroyed if they fail by 10 or more. (Frank: is there a reason you suggest 8?)
I am against using BAB, for the same reasons AeroDm raises.
The reason for the specific limit to HD turned that I advocate is that in general undead's CR scales as HD/2. So a cleric would need to double his level to be able to affect the same "threat" to him. I add in the Cha to make it improtant in turning, and put it before the multiplication to highlight its importance and allow clerics devoted to turning to be able to increase their turning ability significantly.
As for the range... I don't know

If we institute a total-HD-limit, the range becomes less of a balancing factor, and I'm considering just leaving it at 60' radius.
Without such a limit, or if a balancing factor is desired nonetheless, I suggest a 30' cone would be relatively limited in area, while maintaining good flavor.
The more I think about it, the less 5'/level makes sense. It's just too weak at low levels and too powerful at high levels.