I think the bar is set too high in the $60K performance car arena for BMW NOT to put a CF roof on the normal M3 (at least as an option).
The CSL will probably be distinguished by more performance-tuned suspension, a higher redline with 40-60 more HP, carbon ceramic brakes, more cooling for engine, brakes, transmission, etc. Ya know, so it can run head to head with a GT3.
With a standard roof with sunroof, the M3 will be 50 lbs heavier way up high. Ugh -- I think they know better.
Driving sideways: It's not faster, but damn it's more fun!