Vert performance figures are half way between m3 coupe figures and 330i Zhp figures. There's a bigger weight difference between the vert and coupe M3 than there is between the csl and m3 coupe (and weight is what makes the csl the car that it is).
For some people verts are worth it, but there are real and significant downsides.
Significantly smaller back sear
Significantly smaller trunk
Less rigid chassis
More to fail
Not allowed on track with most groups (including BMWCCA)