RE: How do I increase my top speed?
For top Speed, use 19/23t for pinion gears, and 41/45t for spur gears. You could also try 37/41t for spur gears, which will give you even more top speed, but the stock configuration of the RS4 wont let the pinion gears mesh with spur gears this small, so you would need to make some modifications as well.