No doubt SLI 8800GTS G92 will smoke one card at that resolution in most games.
But like everyone is saying, you should probably start with one card and see if you are happy that way. In most games you probably need fsaa to stress one 8800GTS, even at that res. But there are some games like crysis where a single card won't cut it for high details at that res. Still for those that do SLI, you can crank eye candy beyond what one card can handle. Example is [H] where in COD4 they could enable 4x trss aa and have a minimum of 40 fps with SLI. With one card it was 4x MSaa with a low of 26 fps. Not everyone will appreciate the higher level of aa or the 26 vs 40 fps min difference. COD4 is so amazingly efficient it's not a great example really.
http://enthusiast.hardocp.com/article.html?art=MTQ3NSw1LCxoZW50aHVzaWFzdA==
http://enthusiast.hardocp.com/article.html?art=MTQ0OCw4LCxoZW50aHVzaWFzdA==
You may also want to note in the 8800GTS review, in LOTR online, max details at 19x12 no fsaa is not playable on one card. Unfortunately they didn't test that game in the GX2 review, so who knows if the SLI solution would do better or not. Potentially yes, but it's a not tested. You would have to search for proof SLI makes a difference in that game if it's of interest to you.
Oblivion there is a huge difference outdoor between a single G92 or SLI G92. But you'll really need 4xaa/16xaf if you want to hurt the single card and make a big difference in gameplay not just measured fps. Even then, it will only be the most GPU demanding areas where a single G92 hurts, such as waist high grass (foliage) outdoors.