I can name at least two people here in Sweden that dont mind using their M3 CSL on normal roads because they find the comfort to be acceptable.
And if you think 996 GT3 is a comfortable car think again. Personally I think 996 GT3 is too noisy, too much windnoise and roadnoise and you feel every bump in the seat. I wouldnt mind owning a 996 GT3 but as a second car.
CSL is just like GT3 and GT3 RS, doing great on a track but still acceptable for the road. Personally I wouldnt call M3 CSL and 996 GT3 comfortable cars but they do work for normal roads but I understand if someone don't agree with me.
PS
I hear the 997 GT3 has a lot better comfort and works a lot better for daily-use than the old 996 GT3.
It sounds like 997 GT3 got softer suspension than 996 GT3 and thanks to the semi-R-tires the 997 GT3 beats the 996 GT3 around N-ring. Mind the last part is only a speculation from me.