I don't want to sound too cynical, but I'm not sure if I buy into all this G-Power stuff. Didn't they claim something like 800+hp for their M5 supercharger at some point? Now they're down to a more conservative 730hp. Also, that car failed to run at a high speed test sponsored by Continental tires, and it appears to have been plagued by various problems since its birth. Not to mention the kit is something like 185,000 euros (including the car). I think this M3 kit has a long way to go if they still haven't perfected the M5 kit they've spent years on.
On a side note, I was just reading last months BMW Car magazine, and the G Power M5 featured has a front BBK but stock rears. How can you cheap out on a showcase car like that?