Have a play about with some of these tweaks.
It is a multicore game, although as its based on the Oblivion engine which was sorta kinda multicore i would question how much a quad (natural upgrade) would improve your performance.
To reassure you, mine is pretty similar and i run the game fine.
Btw you done all the usual defrags and virus scans and such? Not got any crapware running in the background?
I ran it fine on lower specs than you but ran fine at 1280x1024, max everything. It ocassionally slowed down, which I discovered was because of azureus running. After closing that, everything was smooth.
Have a look at your processes running and see if anything is stealing your speed.
Other than that, try what pr2thej says. Virus scan, defragment, upgrade to 8.12 drivers.