I have both and the 30C perform slightly better. They keep a higher nominal voltage. Also they will last longer because they have to work less hard, relatively.

Zippies are good packs. My oldest pack is now coming up on 200 flights, and though it doesn't perform the way it did when it was new, it's still very usable. I suspect I'll get around 250 (total, so about 50 cycles more) cycles out it before I decide to retire it.