Mister Quickie

I've been reading up on the differences in sound, performance etc but nothing that addresses overall reliability, RMS, IMS, engine failure, etc.

Any input?

extanker

gen 2 seem to be worry free with the 2.9

Spokayman

Since you have listed concerns with RMS and IMS, I assume you are asking about the gen 1 ('06-'08) Cayman engines and not the current 981 Cayman generation. The current 981 generation engines have a different design which eliminates the IMS, and RMS issues seem to have been resolved earlier as well.
The two gen 1 engines are essentially the same except for cylinder displacement and therefore have the same design for RMS, IMS, cam chain, AOS, tensioner, etc.
I have never read anywhere about specific differences in reliability between them. If people bought their Cayman to track or race, most would be using the 3.4 and so there are probably more 3.4 failures based on that kind of use.