a 7950 will leave you with £300 or so pound to spend elsewhere so a more well rounded build would be
i5 3570k £168.89
Asus P8Z77-VLX motherboard £80.06
Corsair TX 550M £66.73
Asus GTX 650 Ti £121.97
Gskill ripjaws 8gb 160mhz £34.55
Seagate Barracuda 500gb £44.75
Corsair carbide 300r £59.99
Coolermaster hyper 212 evo £27.95
Corsair AF 120 dual pack £17.33
Corsair Force GT solid state drive £61.01
Total £683.03
A bit over but a much more well rounded build than anyhing in that price range and a 7950