MMM 6s vs. 4s

personally i think 6s is an all around better set up. Things will run cooler. Your speed all depends on your motor selection.

For bashing and showing off a faster rig would probbly be better as peoples eyes will do this -> O_O
For racing, you really dont get too close to 45 as most tracks are technical...not long straights.

INSANE UNRELIABLE STUPID FAST SPEEDS go for a 1515 1.5D
but Brains 1515/2.5d or 1515/1.5y and jayjays 1515/1y selection would be a good reliable set up.

What speeds are you looking for?