I have a 2004 SL600. KLEEMANN says they have an ECU upgrade that does this:

Thank you for contacting KLEEMANN USA! We currently have ECU upgrades available for your SL600 which will bring it close to 65 AMG specs: 620 HP and about 715 lb/ft. of torque. This consists of a simple engine ECU program which increases peak boost, re-writes the boost map to make more boost available earlier in the RPM range, modified fuel and ignition maps, better throttle response, and a top speed limiter of 186 MPH. Our ECU upgrade is priced at $5,995.00 plus $40.00 for insured, overnight return shipping.

Concerns are this:

Are these guys a good aftermarket company?
What about the factory warranty.

Other than that is is tempting, lots of bang for the buck.

Scott