joe462140 :
i have an i7 930 and am looking to upgrade in the £200 - 400 price range. any suggestions? i was going to get a 2600k sandy bridge but they do not work on the Asus P6X58D
Upgrading your CPU is not going to get you better gaming performance. Games need powerful video cards, not CPUs.
The GTX 670 falls within your price range, and is the undisputed king of value in the high end video card space. As long as you've got a decent 500W or higher power supply, you should be able to run it. If you post what video card you're currently using, we could tell you how much of a performance boost you could expect to get from a video card upgrade.