Higher KV is faster with the same amount of voltage. KV= RPM per volt. The higher KV motors/lower turn are more for onroad(5000+) and lower for off road ofcourse. I would recommend a lower KV motor and gearing up for speed. Higher rated motors run hotter, pull more amps from your battery and give you no room for gearing. The lower rated motors are much easier on your esc and batteries. You can easily gear up or buy higher cell lipos to get more speed. For 2wd trucks 540 works, for 4x4 540 would work, but 550 would provide you more torque and run the heavier truck more easily.