Agree the order is SRT Coupe > SLK32 with top up > SRT roadster. But the differences come down more to the driver than the car and all are hampered by the automatic. In an autocross or tight road course I'd match my 6-speed Crossfire Coupe with UTQG 100 tires & Wavetec against any of the above.

SLK is more of a boulevard cruiser and I prefer to the roadster for two reasons: retractable hardtop and more leg room. Otherwise the two are identical (well the SRT has more fender flares for the larger tires - stock Crossfire wheels and tires on an SLK hit the rear fender lips.