I assume you are also going to get a new monitor?? An HD6870 1GB will probably run almost any game ATM at 1440X900 or 1680X1050 using decent settings
AFAIK.
Edit!!
I have come up with the following components list which also uses the free Scan postage.
The motherboards is a bit basic for an 870 motherboard as it is not the best for overclocking and has relatively few audio outputs. However, it does support AMD Bulldozer,has all solid capacitors and has USB3.0 and SATA3.0 ports.
The HD5770 1GB will be fine with many games at 1440X900 and 1680X1050. More demanding games may need some of the settings turned down a bit at this resolution. At 1280X720 an HD5770 1GB will probably be able to run most games at maximum settings. Maybe,one of the few games it can't max out would be Metro 2033 but OTH even £200 graphics cards can be challengedby this game!!
The next card above it would be a GTX460 1GB and then the faster HD6870:
http://www.scan.co.uk/products/1gb-m...ores-dvi-mhdmi
http://www.scan.co.uk/products/1gb-m...x-dvi-hdmi-mdp