I bought an E92 M3 before the 911. Test drove it, paid my deposit, went home. Got home and didn't feel remotely excited about the car so went back to the dealer the next day and got my deposit, which went straight on the 911 instead.
They're great cars, very capable and a good all-rounder, but as a fun car to drive they do nothing for me sadly.
There never was a Cayman 3.2 only the 3.4, and at a budget of around £21K then you'd be looking at a solid 987.1 car. Very very good cars, but be aware of IMS issues and go in with your eyes open. Aside from that issue, they're the same as a Zed to run but better on fuel, and are a better car all round as long as you get a good spec one (i.e. if it has the 19" wheels, then it MUST have PASM. Most do, so dont worry too much). Sat nav is useless so you'd be better off getting a car without and look for better options.