Single card upgrade for 2 x HD4850 512MB in Crossfire?

[sidnitzerglobin]

So I'm looking to upgrade my main box in the near future (specs below) but am a bit lost what single card solutions are going to provide a significant enough upgrade today and be future proof enough to last me ~2.5-3 years running @ 1680x1050 relatively maxed out to be worth the cash

C2D E8500
Asus Rampage Formula X48
2 x 2GB Corsair Dominator DDR2 1066
2 x MSi HD4850 512MB
Creative Audigy 4
3 x WD Raptor 72GB RAID0
2 x Seagate Barracuda 3G 1TB RAID1
Corsair 750W PSU
Lian Li PC-70

I'd kinda prefer to stay w/ ATI but I guess am not totally averse to going back to Nvidia if there's a compelling advantage.

Looking at the Graphics Card Hierarchy chart here on Tom's I'm seeing the 4850 X2 on the same tier as a 6950 (which is more than I'd like to spend for single card). I'm assuming the 4850 X2 they are referring to is the integrated dual GPU single card model which had a bit better performance than a 2 x 4850 Crossfire solution but not all that significantly better than what I've already got IIRC.

Do I really need to go up to a 6970 to reach a significant jump in GPU horsepower over what I've got now? If so, I think I'll concentrate on getting an i5 Sandy Bridge or LGA1366 i7 mobo and CPU and 8 or 12GB of DDR3 before I worry about GPU upgrades.

 

[sidnitzerglobin]

Kind of answered my own question via experimentation. I wound up grabbing an MSi Twin Frozr II 6870 1GB last night on sale, and while I haven't had the chance to run any empirical benchmarks (aside from WEI), my early subjective assessment is that it's an incremental increase in performance worth the ~$150 I put into it.

It didn't seem to have any issues pushing a stable 40-45fps @ 1680x1050 at stock clock in what I got to see of Skyrim just short of maxed out (Ultra setting w/ distance character detail bumped back to high and AF @ 8x instead of 16x) under Windows 7 SP1 which I imagine should be plenty good enough for most of what I like to play for the next year or 2.

I was toying w/ the idea of going ahead and picking up another for Crossfire, but I'm thinking I might be slightly bottlenecked at the CPU as it stands so I'll probably wait and see where I'm at after I do a mobo/CPU/memory upgrade.