Even my phenom II X4 @ 3.4GHz was a bottleneck on my hd5870 in crysis >< I never really noticed how badly i was limited until i got my i5-2500K and dialled it up to 5GHz

That is very unlikely, but interesting nontheless.
To check for a bottleneck, install a Hardware monitor and check the GPU usage during gameplay, if its reaching the 95%+ area, you either dont have a bottleneck, or its negligible.
On the CPU vs GPU on CryENGINE 3 topic, i think GPU will be totally dominant in the matter, as it was with CE2.
For medium~high anything above a 3.2GHz Dual-Core shoud be fine, the GPU will limit the performance. For enthusiast setting you will need more GPU power, then a quad-core might be necessary.
I know what a bottleneck is and how to check, obviously or i wouldn't have said it was the cause, the hd5870 was running at ~60-75% in said situations. The reason for the slowdown (20-30fps) was usually when a lot of enemies were on screen (end of first level on warhead, village in second level of crysis 1 are the two main points where it noticeably occurs) so the physics/AI thread hit the roof of one core on enthusiast. Crysis 2 was only designed around 2 cores, so the physics runs on one thread, the other 3 cores weren't doing much at all. It's more a coding issue than hardware.
My new i5-2500K at 5GHz has no such issues with one core getting overburdened as all the cores are so much more powerful, so they can brute force past it.