HardOCP  has pit Intel and AMD against one another in a head to head real-world gaming CPU comparison using two BFGTech GeForce 8800 GTX video cards in SLI. Here's a taster:

In Medieval II: Total War we experienced a smoother gameplay experience with the Intel Core 2 Duo X6800, especially with thousands of characters onscreen at the same time. With the AMD Athlon 64 FX-62 we had to reduce the character detail as well as the antialiasing setting. These two games were by far the largest differences we saw between both platforms. They greatly demonstrate how SLI needs a fast CPU to feed it at high resolutions.

Battlefield 2142 also showed us a distinct performance difference, but the framerates were so high that it didn't matter. We were consistently experiencing framerates above 60 FPS with the AMD Athlon 64 FX-62 at 2048x1536 with 16X TR SSAA. That is quite incredible; 16X TR SSAA at 2048x1536 and above 60 FPS! F.E.A.R. Extraction Point, Need for Speed Carbon and World of Warcraft showed us smaller differences that simply translated to no true differences in-game.

Two BFGTech GeForce 8800 GTX in SLI prove that you will want the fastest CPU you can afford backing them. The last thing you want is your large dollar investment in multi-GPU performance being held back by your system configuration. You will be spending well over $1,000 on the graphics subsystem alone and when we are talking that amount of cash you want to be sure the CPU can power your video cards to the fullest.

There is no other way to slice it; our gameplay experiences clearly show the Intel Core 2 Duo X6800 to provide real tangible improvements over the AMD Athlon 64 FX-62 when running GeForce 8800 GTX SLI. The BFGTech GeForce 8800 GTX SLI platform is one seriously fast gaming platform, and the Intel Core 2 Duo X6800 powers it better. As performance moves beyond the GeForce 8800 GTX , we are really going to need impressive CPUs to keep up with multiple-GPU configurations.

As new games are released this year supporting multi-threaded game engines using two or more threads more efficiently, the type and performance of your processor may impact your gaming experience in a very real way as it looks like quad-core gaming and beyond will soon be a reality

In other news, TechReport take an in-depth look at performances offered by the GeForce 8800 GTX and GTS while under SLI. What is the final result?

You really do need a four-megapixel display like the Dell 3007WFP in order to take full advantage of GeForce 8800 SLI with today's games. Even then, a single GeForce 8800 GTX is often fast enough to drive a 2560x1600 monitor quite well without the aid of a second GPU-witness our test results in Quake 4, Half-Life 2: Episode One, and even Oblivion. Heck, even the G80's CSAA 8X and 16X modes have so little performance penalty, one doesn't really need SLI for them. The big exception is Rainbow Six: Vegas, which is brutal at 2560x1600 on everything but a pair of 8800 GTXs. As the first Unreal Engine 3 game we've tested, it may be an indicator of things to come, but I'm not quite sure. It may also just be a lousy port from the Xbox 360. That said, more intensive games are always coming, and there will likely be a reason to upgrade to a second GeForce 8800-even a second GTX-at some point in the next year or so. For now, though, you may want to keep a PCIe slot open and wait.

That said, I've played through decent chunks of both Rainbow Six: Vegas and Oblivion with a pair of 8800 GTXs in SLI on the Dell 3007WFP, and it's a glorious thing, having smooth-as-glass frame rates with incredible image quality on a massive, detailed display. If you have to means to treat yourself to such a setup, the visceral experience certainly won't disappoint.