Crysis 3 cpu bottleneck?

7870 and 1045t @ 3.5Ghz

Sounds like it, that is way too low for a Radeon 7870.

You should check the CPU usage during gaming, HWINFO64 is a great tool to do so. If it's at a constant 100% while gaming, then you got yourself a bottleneck.

You could also by using a rivatuner server show usage, clocks, memory used - Everything in your PC - On screen screen while gaming.

This guide will help you through:

http://www.overclock.net/t/1229915/how-to-cpu-and-gpu-u...

thanks man... great bit of info there

much appreciated  

if your trying to run at more than medium then thats your issue.
the game is a monster for requirements. to max it out you will need a titan, a 690, a 7990 or 2 680's
even 2 gtx 670's will struggle to get up to 60 fps.
crysis 3 does like high thread count cpu's but it doesnt care about speed as long as there over 2.6ghz.
so my guess is your running it at to high a setting that your card cant handle.
try running at medium with fxaa rather than smaa

It need not be a bottleneck. Lower the Resolution, and play the game on lowest, and see if the fps improves. If it does, it might just be that the game is not well optimized to use all your GPU Raw power.