All 1/8 scale buggies can do 40'ishMPh. Some close and some over.

A lot of people here post just the opposite of what I am about to say here:
Bigger engines does NOT mean you go faster. You can get more power low and top end out of a good 21 than you can any of the 25's and 26's on the market. The bigger engines do tend to have a lot of torque and not as much top end.

But if you spend the bucks on a good RB Convept or better engine, you can get mre power out of it than the bigger engines. I have a Force 25 and it does not have the top end that i expected. It does have loads of low end. I get 10 - 12 min run time out of it. Depends on if you WOT or just putting around.