Alright you've come here to ask for criticism on your build. We give you some things that you could change and you decide to hang onto your decisions. That's not a problem, but that defeats the purpose of this topic.
Be aware that SLI also brings extra energy use, heat dissipation and noise. If you like the idea of twice as much junk out of your case for maybe a 5% performance difference, no-one is going to stop you. It doesn't matter how much money you make, you just need to ask yourself whether you think it's worth it, and if you don't know, you ask others if they think it's worth it.
Same with the motherboard. If you want to hang onto it, no need to post it up for criticism. It's a nice board and all but the chipset has lots of problems I've heard; so many that I personally wouldn't touch it. If all you want is to hear whether the build is compatible then I'll answer you yes.
Here is a link for you
that compares 8800GTS SLI with 8800GTX. I suggest you skip the 3D Mark scores as they're just scores from test situations that aren't quite practical. Look at the game benchmarks for a fairer view.
I'd also like to point out that anything above 75fps is useless, since your monitor can only run at a 75hz refresh rate (75fps visible) or 60hz (60fps visible). The SLI 8800GTS gets some nice scores in that benchmark here and there, albeit nothing you'd notice.