Ian could you tell me how far your E Revo moves on one full turn of the motor, trying to work out the gearing for my electric MGT i might only be able to get a 46t spur gear in without some major mods or making serious transmision mods

18.58mm per rev.

That is fairly low as the HV4.5 is high revving. So if you're looking at 4s LiPos and a gruntier motor you can probably get away with higher than that.

Have you seen this speed calculator?

http://www.scriptasylum.com/rc_speed/_top_speed.html