The 600SL rotors are directonally vented and slighly larger in diameter. However, I don't believe the pad is much larger in surface area than the 500E pad.

The rotors & calipers are significantly more expensive.

If you're having fade problems, you need to bring cool air to the rotors/hubs. Invest in getting brake ducts from the front spoiler to the rotors/hubs.

If you're having warping problems, I believe Dean or Michael is having luck with cryogenically-treated rotors. I can't remember which pad (Carbo-Tech, PAGID, etc.) they're having good street performance with. If you're brake-lines are more than 10-years old, replace them. If you go the stainless-steel braided route, be sure to get ones with a plastic sleeve to keep dirt from getting in the braid and causing premature failure.

Most of all, if you want to stop in shorter distance, get wider and stickier tires.

:-) neil