I think it was 125kg Dave, but that was for a no-options car, so most specced with Xenons, Air-con & radio are about 90-100kg lighter. However, weight loss wasn't really the aim, it was lowering of CoGQuote:
Originally Posted by Dave
The list of differences between the two cars is extensive, and not just an airbox & carbon roof as many seem to assume - the whole character of the car was changed
One other point - the price differential between the CSL & M3 was proportionally far smaller than it is between GTS & M4