Given how different a Cayman is from a 911 C4 Cab, maybe figure out if you want
1) Mid engine vs rear engine
2) Open top vs closed top
If still not clear, then take the two samples you found and go for a test drive.
300hp 911 vs 260hp cayman
Mid engine lightness in response vs rear engine tail heavyness
In the end, either choice hardly seems like a punishment
Or one of these instead.. combining the two -
http://forums.pelicanparts.com/porsche-cars-sale/1041674-2005-porsche-boxster-s-6-speed-gt-silver-n-california-car.html