I think the weight reduction goes a looong way, the clk is the the lightest Benz next to the SLK I believe. Weighs around 3600 lbs stock which is less than the newest m3, and I think I have about 200 lbs of more weight taken out of mine. I need to weigh and dyno it! I finally did a writeup on the car for the Mercedes guys so I will share it here too:
Weight Reduction:
OEM hood replaced with VIS Carbon Fiber Hood
Spare Tire delete / Toolkit delete
Aluminum Sheet Metal trunk floor
Trunk Lid carpeting/trim removed
Center Console removed
OEM carpet removed and replaced with lightweight carpeting
Exterior:
Custom Widebody Front and Rear w/ Paint
CLK63 Front Bumper
CL63 Rear Bumper
Trunk Lid Spoiler
All chrome painted black
Wheels, Suspension, Brakes:
20" HRE P40s with 255 and 305 width tires
Bilstein PSS9 Coilover Suspension
Renntech GT BBK: 14.2" 6-piston Front, 13" 4-piston Rear
Power Delivery:
ALL NA 5.5L Motor + 7-speed transmission
Renntech Short Tube Headers
Renntech Dual Exhaust (Quad-tip)
Renntech ECU
Interior:
CLK63 Black Series Steering Wheel w/ Shift Paddles
Suede Headliner
Suede Accents
Renntech Badge on Ashtray Door
Estimated Weight: 3400 lbs
Estimated Power Output: 425-450 HP