Talking about C rates and punch completely ignores the whole point of a C rating. It is nothing to do with punch! A 30C pack isn't any faster than a 20C pack...
Just because your battery can deliver a lot of current, doesn't mean your motor or ESC will draw it. If your battery is so poor that it can not supply enough current and thus your punch is reduced, it means your are operating your battery beyond its limits and is potentially VERY dangerous.
Never ever use a low C rating to reduce performance, use a slow motor, steady thumb or radio/ESC limitation.
For my explanation of C rates:
http://www.glypo.com/guides/lipo/