I've driven my CSL on track for 3 seasons now and feel that i can hustle it around at a reasonable pace at least.
I still get normal M3's that occasionally pass me at the Ring but such normal M3's have either had extensive modifications (Cup tyres, BBK, re-map, airbox, weight-loss and are often caged) or they're being driven by a very good (or very crazy) driver!
The bottom line is apart from some choice brake modifications (pads, braided lines) the CSL is very, very good in standard form, sounds special, and certainly feels very special, and will stand up better to depreciation over time than a standard M3. If you plan on keeping her for many years - buy a CSL.
I like my CSL