What are you using the machine for?
If it was an editing rig with a moderate gaming capability, pretty much nailed it.
If its just a gaming machine, you can downgrade the CPU and RAM, then invest the cash into a stronger GPU.
It'll be used primarily for gaming. Which GPU would you recommend? the 7950 perhaps? do the prices i've sourced seem reasonable for the components? Also out of interest anybody have a view on which OS I should install. Win7 or 8?
Get a 3570k and halve the RAM to 8GB. That should save ~$150 (not sure how much in pounds).
Which is nearly enough for a HD7950.
Havent used Windows 8 yet so I cant really advise, but from what I have seen, there is functionally no difference between 7 and 8. Just a new interface, whether Metro is a dealbreaker or not comes down to you.