Unless it's going to be a track car, consider a Cayman S with PASM instead of the R, even better a black edition.
I considered the R, but for a DD I wanted some creature comforts (ventilated seats, Nav/bose/XM, PASM). I prefer the look of the S vs the fixed wing on the R, the fabric pull straps on the R are goofy and I wanted the extra sound deadening. The R only has 10 more Hp and the same torque.
Doesn't make sense to me to get the R and add all the weight back in with radio and A/C. If you still want an R, make sure you sit in the sport buckets to make sure they are ok for you, there is no seat back adjustment.
I didn't consider the C63, but did consider an M3, great engine, but still looks like every other 3 series out there.
Do you want a hammer or a scalpel?