Assassin's Creed 3 low fps with good PC

[mpaul07]

I get only 20 fps constantly in Boston on the lowest settings 720p and 10-15 fps with EVERYTHING maxed out at 1080p. My specs:
Q6600 2.4Ghz (no, I can't overclock since I have a stock cooler)
4GB Ram 800Mhz
r9 280 3GB

I know the CPU is bottlenecking the GPU a lot but I expected more than 20 fps since it runs on my laptop at 720p, medium graphics at 30fps (i5 3230M 2.6Ghz, Radeon HD7600M, 8GB Ram 1600Mhz). I was thinking it could be because of the slow ram but it is still weird since I can play AC IV Black Flag with everything maxed out and get 30fps no problem.
I will buy an FX-6300 and 8GB RAM soon. What kind of performance improvement can I expect?

 

[RaDiKaL_]

Its the CPU, I had the same CPU oced at 3.4Ghz with my current video card (HD4850) and used to get 25-40fps with high settings @1280x1024, once I got my FX-8320 with the same video card my FPS jumped to 33-65 with same quality settings.

AC3 is not as well optimized AC Black Flag is, hence its poor performance, your new rig should yield far better than mine due to your R9 280, I'd say 60+fps @1080p, with some drops to around low 30's in AC3 due to its bad optimization for PC.