The question is in the title should I go for 6850's in crossfire or a single 6950.
Here are the cards:
6850's - http://www.amazon.co.uk/XFX-Radeon-HD6850-Graphics-Memory/dp/B0047ZH7FU/ref=sr_1_6?ie=UTF8&qid=1343398057&sr=8-6
6950 - http://www.amazon.co.uk/XFX-Radeon-Graphics-Dual-DVI-DisplayPort/dp/B0057PW7A4/ref=wl_it_dp_o_piT1_nS_nC?ie=UTF8&colid=3HE27JDOPUYVW&coliid=I2K614OWZZPW03
Here are the cards:
6850's - http://www.amazon.co.uk/XFX-Radeon-HD6850-Graphics-Memory/dp/B0047ZH7FU/ref=sr_1_6?ie=UTF8&qid=1343398057&sr=8-6
6950 - http://www.amazon.co.uk/XFX-Radeon-Graphics-Dual-DVI-DisplayPort/dp/B0057PW7A4/ref=wl_it_dp_o_piT1_nS_nC?ie=UTF8&colid=3HE27JDOPUYVW&coliid=I2K614OWZZPW03