My opinion is for you to stay away from the 4200 cell. It lacked serious reliability, however the 4600 IB's were better or consider the EnerG 4600's. If I was choosing I would go with the EnerG's myself.
Either of those would be a better fit for you.
Team ORCA / ORCA USA / Pro Spec
Serpent America / Team Serpent S411 ERYX / On Point Racing OP12C, S120 / Xceed Products
Hangar 30 / Seattle RC Racers
Fasttrax Racing Series / NORA On Road Series