E-revo 6.5 novak

use Brian G's speed calc...
http://www.scriptasylum.com/rc_speed/_top_speed.html

If by when you say you want more torque you mean you want more punch when you pull the trigger then lipos would be a good option (you can pull more amps with Lipos).
In order to figure out top speed you would need to know the tire size and the KV of the motor. I know Novak rates their motors unloaded so it effects the number the speed calc spits out a bit.
Last year I calculated my novak powered buggy should go around 46mph using the calc, I time trial it (100ft straight line) and it clocked around 44mph... so it is pretty close.

An MMM would (possible) give you more reliablity (it seems with an MMM if it is going to fail, it should fail soon, where as Novak's are more sensitive and could go at any time if you push it to hard).
Check out the speed calc, go from there. Lipos would probably be the next (logical) step for you.