The only experience I have is as a passneger but the 4 seat rzr was not much slower than the 2 seat rzr. 4 seater had two guys in it. 2 seater had 1 guy, 4 seater slowly lost one rzr length over approximately a 1/4-1/2 mile at most.
Everything else mr. green said is right. He is an expert just like me. He may be more expert than I am.