[nutz4sand]

With a little careful shopping (and maybe a bit of time) you should be able to find a deal on the bigger motors like the 1000's and 1100's etc (in case your not brand specific.) the larger than that group (hayabusa and zx14 are gonna be $$$ unless you find a steal (literally).

The smaller motors will work but the bigger motors will of course be better. One thing to keep in mind is gear ratio (and tire size as it relates directly) The smaller the motor the more deeper the gearing it will NEED or it will suffer. The larger motor will pull higher gearing better but still the deeper gearing will keep the power flowing better no matter what the engine.