Help me decide on a high-end graphics card

I'll be forward with my thoughts about one thing right from the start - Pricing.

I don't think ATI cards are going to drop in price. They have been proven performers within their current price ranges for up to 6 months now. Fermi's arrival may see some very slight shifting, but I do not believe there will be a drop in price for some time. Why? Because ATI's cards offer excellent gaming performance, vastly superior energy conservation, unique single-GPU Eyefinity, and excellent overclocking headroom. I really don't think we'll see any major shift until nVidia brings more to the table than the 470 and 480. Though we may actually see 5850's fall back under and at $300 permanently if the 470 comes in at ~$350. This would obviously make the 5850 the more affordable choice.

That said, for the price difference between two 5870's and one 5970, the choice seems rather obvious - ~$850-$900 for two 5870's, or ~$700 for a single 5970. How's that obvious? Well performance-wise, they will sometimes trade blows, with dual-5870's taking the lead most of the time. But the differences in performance tend to be rather slim in almost all cases. So from a performance per dollar standpoint at this very moment, 5970 wins. At least it, will once they're actually in supply again.

In terms of future upgrades, your options are likely to be much more limited with a 5970, as it has not been, nor will it ever be produced in the same quantity as single 5850's and 5870's. (We see this already...) This means that adding another one 6 months, a year, or two years from now may be far more difficult than finding one is right at this very moment. It could also be quite costly, as the cards themselves would become unique due to their lower production numbers. Also, take into account that in order to get the full potential of a 2nd 5970, you would have to have an X58 or 790FX (890FX when it's available) motherboard, otherwise both cards would use x8/x8 Quad-Fire, leaving x4 per actual GPU. (More on this later.) I feel the advantage goes to the 5870 when it comes to future upgrade options, which would include not only Quad-Fire, but Tri-Fire as well.

When I weigh the two options, and discount the obvious price advantage I first pointed out, I prefer the two 5870 (or even 5850) option for a few reasons.

1. A 5970 is a dual-GPU, single-slot card using a single PCIe x16 slot. This means you're getting an equivalent to x8/x8 CrossFire. In an X58 or 790FX motherboard (and eventually 890FX) using two separate cards, you'd get x16/x16 CrossFire using two 5870's or 5850's. Yeah, I've read all the arguments that have been made about it not having a "noticeable" difference. Yet the difference remains - 16 channels per card, or 8 channels per card. (Or even 4 channels per GPU with a dual-5970 config not on an X58 or 790FX motherboard.) These differences can lead up to a 2-7% performance gain, according to Anandtech: http://www.anandtech.com/mb/showdoc.aspx?i=3649

2. Previously mentioned upgrade options and availabilty.

3. Peace of mind. One thing that separates the two choices is the impact of a card failure. If anything goes wrong with only card you have, you're SoL til the replacement arrives. With multiple cards, should one die, you'll still be able to use your computer while waiting for a replacement.

4. Cooling. It's much harder to keep multi-GPU cards cool than it is single-GPU cards. This can affect overclocking potential.

5. Overclocking itself deserves a spot, as single-GPU cards tend to OC better.