Need help choosing GPU for new gaming rig

Yo GS users, im in the process of putting together a gaming rig and so far all my components have arrived besides the gpu since the model i originally ordered was OOS. So far my rig consists of the following:

Intel CPU Core i7 2600K Unlocked Sandy Bridge Quad Core Processor (4.7ghz)

Asus Sabertooth P67 Rev3 Intel P67 Express Socket 1155 Motherboard

Corsair Memory Vengeance 8GB DDR3 1600 MHz CAS 9 XMP Dual Channel Desktop

Corsair Enthusiast TX V2 CMPSU-850TXV2UK 850W Power Supply (PSU)

The gpu i originally planned on was a £200 ASUS 6950 2GB which i intended to unlock to a 6970 via the bios switch however this model is OOS and im finding it hard to find a site stocked with 6950 reference boards besides the XFX Model. Should i go for the £200 XFX 6950 2GB or a £240 sapphire 6970 or a £190 GTX570ti or something else entirely. Also by the end of the year i plan to add a second gpu of whichever i choose to run in either sli or crossfire. Help would be much appreciated as all the different options is pissin me off. So far ive searched scan, dabs, ebuyer and yoyotech for UK delivery, any websites with good offers on gpus would be great also. Thanks in advance.

I would go for a fast single card like a 560ti, 570, 580. Thats what I did anyway and I am glad with what I purchased, the 6950 is great value for money though.

A 1GB 6950 performs almost identical to a 560 ti, why switch? If anything get a 570/580

I read it as you had a 6950 already for some reason. oops...

the 6950 is still the best of the bunch, even without the bios switch. Either the 1gb or the 2gb are fine. If you want to get the 560 ti then I suggest searching local ads for it, I found alot of people are dumping them for cheap. I was offered one for a flat price for $190, , but decided to go with the 460 1gb for $100 instead :D

Id look at the 570, you can pick a nice evga one from scan for about 230£.