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I would say a 7850 with a healthy overclock should give you a nice jump in performance...
http://www.overclockers.co.uk/showproduct.php?prodid=GX-289-AS&groupid=701&catid=56&subcat=411
...or, you could stretch to a 7950. Don't forget you can sell the games to even things out. (A 7850 with games could work out a very cheap upgrade indeed).
http://www.overclockers.co.uk/showproduct.php?prodid=GX-287-AS&groupid=701&catid=56&subcat=1673
I've linked Asus as an example (you mention noise in your post), though there are others that would suit, e.g. Gigabyte / HIS. Iirc, Asus make some of the quietest models in these ranges. However, be warned, they aren't renowned for being the quickest when it comes to dealing with replacements.
+1.
If you stretch even to a £229 7950 and then sell the game codes to get under budget this is the best overall option I think.
On a quick question do you think the prices will drop much more?