Lipo cells are 1/3 the weight of Nimh cells, if i remember right. So even if you build a pack with 4 cells in series and 2 or 3 in parallel (4s2p or 4s3p), it would weigh a ton less than the equivilent voltage in Nimh cells, which allows you to gear higher for the lack of weight, and lets the vehicle accellerate or decellerate faster because there's less mass it has to move. Because the truck weighs less overall, there's also good chance you'll be able to jump further, but that's your call.

35mph? I think that'd be easily do-able with a 7xl and a 9920 controller, you'd theoretically be able to even run 6s lipo on that motor, but that would prob. be too much power (if there is such a thing)........it'd be an amazing sight though. :D