I would strongly suggest an SSD as your system drive (its a night and day difference comparing to mechanical drive in everyday use, it also significantly reduces games loading times, although you would have to go with something like 120GB to install more than 2 games on it along your system). Go for i5 as well, much more future proof option. Also 7870 is a big overkill for resolutions under 1080p. Go for 2gb 7850 instead. This build (no Windows included) is a much more rounded option, it will basically do (almost) anything you can throw at it (including BlueRay playback, high to ultra details gaming up to 1080p). Just my suggestions. Good luck!
Intel Core i5-3470
£145.38
ASRock B75 PRO3-M
£55.99
Corsair 8GB
£29.59
Intel 60GB SSD
£50.97
Western Digital 1TB 7200RPM
£56.94
Gigabyte Radeon HD 7850
£160.54
Fractal Design Core 1000
£32.38
OCZ 500W
£56.50
Lite-On iHOS104-06
£25.88
Total: £614.17
(http://pcpartpicker.com/uk/p/qoge)
Estimated Wattage:
301W