LiPo
Carl, back to your component choices, those are all just fine. Dave might be right by saying any brand 4.5 is going to have some serious zing to it. 6.5 or 5.5 might be a better choice and if you need more power, get a 4.5 later and keep your milder motor as a spare. Dave is also right by saying Spektrum, Futaba FAAST, Airtronics/Sanwa/KO 2.4 systems really save on headaches at larger events and virtually eliminate any chance of glitching. Since switching to the 4000mAh MaxAmps LiPo saddle pack, I will never, ever go back to NiMH cells. I have added some Tungsten weights in the rear to compensate for the lack of weight due to LiPo.
Take the time and browse through the 501X thread in the electric off-road forum on
www.rctech.net too. Just ignore the bmag posts there and here on Jimmy's site PLEASE!
You also PM'd me about a setup. Post what kind of surface you will or are racing on and I'm sure we can help.