Depends on your resolution, your budget, and what you do with it.
If you are a gamer (probably since you already have an SLI rig) then there may be some good options for upgrading if....
You are running decent resolutions, such as 1920x1080 or higher, if you have a decent budget to get anything worth upgrading over sli 8800s, and if the games you play, or plan on playing, require that sort of grunt to achieve 60+ fps.
runining at 1920x1080 on a 46" monitor... so obviously budget has nothing to do with it =). and everything runs on max settings at stable frame rates at the moment, im just thinking about upgrading b/c im wondering if im going to hit a bottle neck in the near future....
To get any significant upgrade right now, you would have to start with a 5870, or CF 5850s. Those cards can be tough to find right now, and are carrying inflated prices. If you are already getting enjoyable performance from your set up, you may not experience any real gain from the investment. If you go with Nvidia right now, you will not have DX11, and will pay even more for the same graphics power.
I say wait until you start feeling your cards choke on the games you play, or you get desperate for DX11 goodness. By that time, there should be better options available.
well upgrade when you HIT the bottleneck, why upgrade now.
Actually noone can stop you from upgrading buy why bragging about it. Noone will give you advice to upgrade, whether you do it anyway is your decision
Sit tight for a little while with those 8800's, when the time comes, ATI will have a 5890 in circulation, that will be the card you want, it'll out-class the 8800's in SLI and also leave room for another 5890 when the time comes. The End.