I was going to try the Quaife Torsional Diff. I've heard from people who have them in their C32s that with the car in Dyno mode (i.e. traction system completely off) it shaves 3-4 tenths off the 0-60 time compared to running with the system on, but the button set to off, which is generally the fastest. The diff isn't officially listed by Quaife to work in the SLK or SRT-6, so I'm going to look into how different the setup actually is.