Well, I'd like to keep it at 6 cells just because after I buy a BL system, I won't be able to afford new batts for quite a while. I think I'll try my brother's 5300/warrior setup and see how it does with that. I'm thinking the 4200 will be about right as it says it has about the same power as a 12T brushed, so that should be a good mix of torque and speed for my application (track hacking and launching it).