The "rovers are too slow" bit has been done to death by now since they got released. People simply don't realize how fast rovers in real life go and how fast 20 m/s is (multiply by 3,6 to get a value in km/h, divide by 1,6 after that to get a value in mph). Also they don't appreciate how less lethal driving in a thick atmosphere and fairly high gravity environment is. When you realize that you realize that going 40 m/s on Duna with a pre-0.19 stock rover was as dangerous as it should have been, especially if your tried dodging the scatter rocks (I know they don't have a collision mesh, wonder if they ever will). With that said if you want to go very fast use the landing gear and rocket/jet engines. Also always remember to keep your center of mass low. The higher it is the easier it is for your rover to start rolling uncontrollably during a turn. And that's something you want to avoid, usually.