That's what I'd get. On the stock cooler I wouldn't overclock it really - maybe just push it up from 3.5GHz to 3.8.
You'd get away easily with 550w. The XFX PSUs are very high quality.
Modular and high quality - I'd get this:
http://www.overclockers.co.uk/showproduct.php?prodid=CA-018-SS
You said £75-90!
thats only 70w more than my current though, which seems nearly pointless.