I would say read my FAQ, but instead I'll say this:
For a sane setup that will give you useable speeds and power, and better runtimes, aim for a 1600-1800kv motor.
That should allow you to gear up or down a bit to get speeds in and around the 40-50mph region I reckons.
I personally will be after a 2000kv motor for 5s lipo use, and will gear down a touch to compensate for my hefty truck; a lighter truck could be geared taller without placing excessive load on the motor or batts.
