Philippe
Don't do it!!!!!!!!!!!!!
....if you want more mid-range/power, that is. I have dyno charts to prove my 916 performed better with a 45mm system than 50mm.
If you just want it for looks/pose-value then great, but otherwise you'd be better off spending your cash on something that will give you a genuine benefit (like some lovely OZ wheels, for instance
- only joking).
Hope that helps