This 2 video card thing may end soon. I wasn't a believer before I decited to try it. You'd think two 8800 GTS 640'S SLI would look alot better than the X1800 XT it replaced. But in looking at most games, I thought the X1800 may have been a bit smoother. Details all look the same but the shades on the ATI seemed to be smoother still as I took the cards out and went back and forth. But the benchies show a whole different story. But for my eyes....SLI isn't worth it. I might send a card back. Any luck with crossfire?...I did that one a few months ago

I'm surprised by this post.  The X1800 XT is still a decent card, but in comparison to 8800 GTS SLI, it's not even in the same league.  It sounds like it's not necessarily average framerates that have you disappointed, but image quality and potentially minium framerates (based on your 'smoother' comment).

The only time an SLI rig may have lower framerates than a single X1800 XT is in 100% compeltely CPU-bound circumstances, because there is some CPU overhead associated with SLI.  In games like this, I doubt you could consider any video card truly "smoother" than another, however.

With the kind of horsepower you've got now, have you tried increasing the image quality and making your comparisons again.  If your single X1800 XT was getting 60fps in your favorite game and the SLI setup is now getting 120fps, and they're both configured for 4xAA and 8x aniso, try raising the settings on the SLI rig to improve image quality - maybe you can now run 8xs AA and 16x high quality aniso at a higher resolution and still get 60+fps.  You should also turn on the high-quality filtering mode in NVIDIA's drivers for the best image quality on the SLI rig.  And also make sure V-Sync in enabled when playing your games to prevent shearing or other artifacts in situations where the SLI rig it putting out a higher framerate than your monitor's refresh rate.

Lastly, if you don't like SLI, you're not going to like CrossFire.

BigWop:

maybe you can now run 8xs AA and 16x high quality aniso at a higher resolution and still get 60+fps.

BigWop:

And also make sure V-Sync in enabled

This feature does eliminate shearing, but can also degrade performace(i.e. cause "stuttering/hiccups") in some games/situations even when you have plenty of cpu/gpu power and ram.