I don't like using technical terms for this subject because it's simply not relevant to most people. Here are my findings in layman's terms:
-Variables: Rear arm length and hub offset. Constant: Arm holder width.
A shorter arm with more hub offset will have more forward traction and the rear will rotate more in corners, making the car feel more aggressive. This is more suited for technical tracks, and the car is normally faster this way. A longer arm with less hub offset will feel a little calmer and more stable and will normally reward smoother drivers. On the JQ car we have this option, and we've found that the short arm is the best to base setups around.
-Variables: Rear arm length and arm holder width. Constant: Hub offset.
A shorter arm with a wider rear arm holder will make the car feel more aggressive, and vise versa will make the car have more traction and feel more stable. Mugen went from the latter to the former from the MBX6 to MBX7, and some drivers went back to the 6 rear end to get more rear grip.