Talk:Prodigious caster (3.5e Feat)
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I'd suggest capping the bonus to be equal to the maximum of the variable part of the spell. I'm currently using this feat on my sorcerer with a CHA mod of 10. This makes spells like Energy drain 2d4+10 levels (12-18) instead of 2-8, and a level 1 spell like Ray of Enfeeblement will drain 1d6+15 (16-21) STR instead of 1d6+5 (6-11). As a player's casting stat increases, this bonus gets insane.
I think it'd be best to limit it for Enervation to +8 (max roll of 2d4) and +6 for Ray of Enfeeblement (1d6) so that you don't end up completely overpowered. This cap would have very little effect on healing/damaging spells so it wouldn't be too big a nerf.