.12 is perfect for touring car though. Its smaller , lighter weight , uses less gas and revs really high.

Generally a larger motor is harder to get to rev as high is going to weigh more and use more gas. But there are some screamers out there in all sizes.

.21 you will be using a lot of gas. Youll be tearing through tires , gears and more and it will be hard to drive. But will be fast.

If you want to be smart but you want insane speed. Get the new os 18TZ the thing has 2hp = monster in a smaller package.