[Bogie]

The 0-60 stats are virtually identical between SLK and RL.

I can't find the actual torque curve on the SLK, but peak torque of 258 is spec'd at 2400 RPM. SLK HP peaks out at 6000 RPM, at 234 torque while the RL peaks out at 5300 RPM at 260 torque.

I guess I'll just say that a torque of 258 vs 260, an HP of 268 vs 260, a HP peak of 6000 vs 5300 and redline of 6000 vs 6300 is so close that the engine performance is a wash. Although the SLK specific torque value suggests a torque roll off beyond 2400, the other performance values suggest the roll off is negligible, giving the SLK comparable torque through the RPM range in that the torque peaks low and is sustained. Hence, it seems like everything goes to gearing and drive train efficiency.

Considering the SLK is heavier, and delivers comparble performance at comparable engine output, I would say the weight is made up in drive train efficiency...horsepower to the wheels. Or, the difference could be close enough to enter turbo lag range. Yes, the RL has almost no lag, but it does have "some" lag. And when two cars are this closely matched in performance, a half second can make all the difference.

Edit: Gear Ratios 1 to 3 (RL/SLK)
1. 3.42/4.46 <---SLK is very beefy off the line. Of course, it will have to dump to second sooner, but it can take peak torque at 4.46 to 6000, while the RL rolls off at 5300...so while the RL will be delivering more torque from the engine, the SLK will be delivering more torque to the wheels, but will have to shift sooner and weighs more. This is a very interesting matchup.
2. 2.21/2.61
3. 1.6/1.72
Final: 3.91 / 3.27