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.