RE: slipper gear
The main function of the slipper clutch is to protect the internal gears of the tranny. When you come off of a jump or when you go through the bumps or off a curb,(anyplace you experience uncontrolled wheelspin) and then come back in to traction, your wheels are spinning at 20-35 MPH. That's quite a shock for little plastic gears in little plastic housings.
The slipper can also be used for 'traction control' in a very loose traction situation. This will decrease performance though. It could also increase your lap time, at the same time.
To properly adjust the slipper, take the body off, hold both rear tires, and push the spur gear with your thumb while rolling rear tires backward. With moderate pressure, your spur should slide on the slipper. Adjustments to that basic setting are as necessary to suit conditions and driving style.
For 'maximum performance', you could run it really tight, but you will probably be replacing tranny gears more frequently.
I have mine set so that I can hear it slip a little bit when the truck is the heaviest, and has the most traction. I can hear it slip a little bit when I come off of a berm, or up the face of a jump when it's pre-loading, and when I land on the throttle.