I think the extra wheels is essential if you wanna go fast, specially in Duna, Tylo etc sometimes you hit the ground so fast the extra wheels helps to distribute the load. Not to mention when some wheels fly out but the rover still works.
Example: after hitting the ground at 150 m/s my engineer and 2 wheels went kaput but the rover is still going strong. Tefrod Kerman didn't even notice.
Exactly, setting SAS to Prograde is a must because you will only have to use Q and E to align the rover when you flip, and you will be flipping a lot specially if you try to slow down using brakes but that's half the fun, if you don't like too much fun you should burn Retrograde.