The medusa 36-60-2000 on 4s will be great for racing then, while both Castle Neu motors may be a little too fast.
I can't really comment any more in terms of what to use for the revo, since I don't have experience with truggies/monster trucks, but I know for sure that the the Castle Neu 2200 will be insane on 6s and better for racing on 4s.
My vehicles (that work):
Custom experimental Losi 810/TEN SCTE - The fastest 1/8 scale buggy on the track - 5.2lb rtr - readily convertable to a ROAR legal 1/10 scale 4x4 SCT.
Custom Losi 8ight - lowest CG of any 1/8 buggy
Losi 22 Mid Motor