If you swap to 2s, you will also need to swap in a proper 2s SCT motor. Something with 4 poles and about 4000kv.
I've heard good things about this motor -http://www.smc-racing.net/index.php?route=product/category&path=112_132
I've heard good things about this motor -http://www.smc-racing.net/index.php?route=product/category&path=112_132