I'd like to know why you are considering SLi/Xfire so much?
Why not just get a newer 6XX series card for a potential $100-200 in saving, have better performance, lower power usage, cooler production, and lower fan speeds?
I currently am using a 5970, and recently did a really nice overclock to my CPU to put it 4GHz, I have it water cooled with a single radiator closed loop system and recently just added 2 Noctua fans to put it in a push and pull config. I did this because obviously single radiator closed loop water cooling isn't the best and my OC brought my idle temps to ~50c with the fans it brought it down to ~40c.
What I had wanted to do was actually get a new video card but decided not to because I've been benchmarking BF3 and in Op Metro I get an average of 119 FPS @1920x1080, all Ultra no AA no Blur -- even though being suppresed is beyond rediculous in the game. What I am suggesting is though go for something new, don't go a single step above what you have now in terms of generational hardware.
You have a 5770 why go for 480's which were good but louder and ran hotter than most cards. And I am also a bigger nVidia fan and my suggestion is to go with a 670 or 680 and down the line if you get multiple monitors push it to a Sli config. Why Sli now with no real purpose when you get get a single card solution that performs better.
This is all my opinion, just simple advice from my perspective. You will decide what you want.
Another thing I might add is with the money you save, I see you want extra fans for your H100, I'd highly recommend getting 4 Noctua fans and put it in a push/pull config, I can almost bet the temps will be amazing. In all honesty I didn't think these fans would help, my older PWM fan would crank up speeds and sound like a jet blasting off when my CPU went up to higher temps. But with these 2 Noctua fans I barely hear them and it keeps my system very cool. The sucky thing is though even with a 92MM fan blowing the air out from the back the idle temps have stood generally the same at ~22-27c but I believe my ambient sensors might be on the frits because when I put my hand in my case it is actually very cool and I don't really feel any warm spots.