Tom's Hardware published an article that outlines a few troubles 3-Way SLI is having with Crysis. Here's an excerpt:

After our initial benchmark tests of Crysis on Falcon Northwest's 3-way SLI Mach V model, we decided to go back for another round of tests using Nvidia's recently released 169.28 beta driver, which was designed to help improve SLI and 3-way SLI performance in conjunction with Crytek's official Crysis v1.1 patch. And after more than a week of extensive testing, we have some good news and some bad news. The good news is, Crysis is almost playable at a maximum resolution of 2560x1600 with all DirectX 10 settings enabled. The bad news is, you have to disable 3-way SLI to achieve it.

If you're scratching your head right now, well, you're not alone. For some bizarre reason, the 169.28 ForceWare doesn't play nice with a 2560x1600 resolution. In fact, as our results show, disabling 3-way SLI and using just one of the 8800 Ultra GPU's inside the Mach V yielded better frame rates for Crysis than using all three video cards. At first we thought we had reversed the findings accidentally - after all, our tests results for other resolutions such as 1920x1200 using the 169.28 driver were quite impressive and saw no such problems. But we ran the tests again and again over several days (and several game and operating system crashes) and confirmed the results.