I'm planning a budget gaming pc build (around £700 or £900) and am wondering weather spending £70 ($65) more on a 6950 rather than the cheaper 6870 is worth it.
Crossfired 6870s will certainly do the job.
And as far as money is concerned definitely get the 6870.
It can be overclocked to match the 6950 in performance, and it can be $60-80 cheaper.
go for the 6950, and the 6950 can be flashed to 6970 performance. Its the way forwards, make sure its a reference card though. I have two 6950 asus reference flashed to sapphire 6970 and its a beast
only reference 6950's can be flashed matey. I got mine from ebuyer.com , it was the asus 6950 reference design, it also comes with a dual bios and a switch so you always have a backup bios
When a chip maker (nVidia or AMD) make a new GPU, they give third parties a "template" we usually call "reference card". So, when they release the cards, they usually carry the good and bad choice calls from the original design. Down the road, 3rd parties usually improve the original design (ref. card) in some areas where they see fit.
In this particular case, the Ref card (template) from the 6950 2GB series had some things "locked", so you could "unlock" them to be a full 6970 2GB.
Now, to the original topic: 2x6870's in rebate or offer are unbeatable. I'm currently using a 6870 from a friend (got 2 from rebate for like 140usd each) and it's slightly better than my 4890 in DX9 at 1080p. I can tell the difference though, plus it handles 1080p quite well in BC2, so BC3 should be enough for a single 6950 1GB even IMO (that's DX11 I'm talking about too).
Yeah the 560Ti has extremely similar performance to the 6950 and these days is cheaper, it's what i'm looking at, was previously looking at 6950 but the prices have gone up and i no longer think it's worth it. Plus they can OC to GTX 570 levels.