So I have about $300 for a graphics card and am wondering which card to get. The 6870's are running at about $270, while the 6950s are running at $300. I am just wondering if the improvement is worth the $30-$40?
Not a big difference, really. Ultimately as you go to more expensive cards, the amount of improved performance isn't relative to the cost increase. I'm only talking about technicalities here but if you look at a GTX460 for $200, it's 50% more to buy the 6950 but the improvement in performance is, what, 15-20%?
So really, the question is what do you really need? What games do you play? What resolution? At 1080p, a 6870 should do just fine. It's slightly better than a 5850, which I had a single one for a while and could play Crysis on high with some AA. Most games these days aren't near as demanding as that, except Metro 2033 and maybe a few others, so IMO you'd be just fine with a 6870 but on the other hand, it is comforting to have a higher end card like the 6950.
One thing I don't know about is how these new ones overclock. I bought my 5850s because they could overclock well, and currently I run them at 875/1200 (up from 700/1000). I think it might be the 6870 - not sure right now - but I read that it already has such high clocks (like 900 core) that you really can't push a big OC out of it.
There should be a 10% average advantage for the 6950, more at higher resolutions due to the 2GB memory. The GTX460 is behind by 24%, but of course, that is for the stock clocked version. Factory overclocked 460's with custom cooling are the norm.