Your cpu is a serious bottleneck for high resolutions, but I'd be looking at your hard drive. Whenever you turn the camera, you are loading all new stuff, which the hdd has to seek out and find hte files for and load.

I used to play on an intel q6600 quad core, really awesome processor with a gtx280 and 6gb ram. My GPU was my bottleneck. When I upgraded to the gtx580, bam, my cpu usage shot to the roof, because the gpu was no longer the bottleneck. When I upgraded to an i7 950, bam, ram issue, hten hard drive issue. Now I'm at 2 gtx580's in SLI, 12gb ram, and i7 950 and 2 high end SSD's, and hte GPU's are the bottleneck again.

Try limiting your fps to 30, that helped me in the past.