I overclock the i7 920 to a very safe 3.66GHz, the RAM to 1600MHz and the 4870X2 to 900/1000.
I currently run it on a single 1680x1050 monitor, and I'm very happy with the FPS of current games at max settings.
I have recently purchased 2 more identical monitors (that makes 3x1680 =5040 pixels wide) and (1050 high) and I wish to run it in a triple screen setup for gaming (5040x1050). These monitors have only VGA and DVI input.
I know that the 4870X2 doesn't support such a resolution. And that is why I am after a new graphics card.
I was initially thinking about purchasing the HD6970 and a Displayport-to-DVI adapter and running the three monitors on that single 6970. However, looking at reviews it doesn't seem to satisfy my requirements (I wish to run games at max settings at 5040x1050 with a minimum of 30fps)
I then thought about getting a GTX590, but that seems to be very expensive (even taking into consideration that it doesn't require a display port to DVI adapter as it already has 3 DVI ports).
I also thought about getting a HD6990, but the noise and the heat (experience with the stock 4870X2 cooler) put me off greatly.
Another option that I thought about was crossfiring my current 4870X2 with a 6970. The 4870X2 would output to one monitor, and the 6970 would output to two.
To summarize, if I want to run games at 5040x1050 at max settings with a minimum of 30fps, what do I need? 1> A single 6970 ($450 including dp-to-dvi cable) 2> A single 6990 ($800) 3> A single GTX590 ($900) 4> Crossfiring a single 6970 with my current 4870X2 ($400)
P.S. The most demanding games I'd ever play is probably Crysis 2, GRID, Starcraft 2, Dead Space 2, Assasin's Creed Brotherhood, Dragon Age 2 etc.
I suggest either two 6970's or two GTX 580's. The 6990 or GTX 590 aren't the best solutions to this. You can't crossfire a 6970 with a 4870X2, they have to be in the same series family (4 series, 5 series, 6 series).
If you're wanting to keep the budget a little tighter, you could go for two 6950's or two gtx 570's, you'll get great performance out of either of these.
What's you're PSU like, it's going to get tested running two high end cards like this.
Two 6970's / 580's would crush the 6990/590. Two way SLI/crossfire is fine, the vast majority of modern games support dual GPU setups and even those that don't can be forced to by the CCC or Nvidia Control Panel.
I will always say to you two 6970's / 580's over a single 6990/590. Even though it's an elegant solution, you'll simply not get the epic performance two 6970's / 580's will give.