Anyway, this whole mess first started back when I first brought 2x GTX 460s for SLI, after reading reviews of how awesome they performed. I had heating issues with mine though, due to the design of the cards, one of the fans of one of the cards was getting blocked by the other card (my case is very cramped, which means SLI'ed GPUs need to be right next to each other). I figured that what I needed to do was get new graphics cards that use the "intake" style of fan like the 2x graphics cards that originally came with my system had.
So what I did was I brought a EVGA GTX 570 SuperClock, which not only had the correct type of fan, but a single 570 was apparently similar in performance to SLI'ed 460s, so I figured that getting a single 570 for now would give me the current power of my SLI 460s and I could get a second 570 later.
Well, I've left it too late, the 570 with that style of fan is out of print. Which leaves me with a sticky situation. Do I:
1) Somehow track down old stock? It's product code is 012-P3-1572-KR, and all the stores I've checked don't have them. If someone could track down an Australian based store that still has stock, that would be awesome (apparently shipping would be around $80 for one of these cards from America, which is way too much)
2) SLI a different GTX 570? I guess I could also try a different brand 570 too? I see that ASUS make a 570 (the ASUS 1280M GTX570) that has an intake style fan, and since you can apparently mix different brands and even keep the faster core speed if one of them is overclocked, this shouldn't be a problem right? Both have 1280MB of RAM, and they both use the same GPU right?
I could always get one of the EVGAs with the new style fan, hopefully this wouldn't be too bad, since I can always use my "intake-style" 570 as the one that would be getting it's fan blocked (if it had the new style fan that is), so overheating shouldn't be a problem for it. However, the new card's fan would be very close to the bottom of the case, so it wouldn't have optimal air-flow.
3) Scrap the 570 and get something else? Like a 580 or something? I guess SLI'ed 560s would be a good option (the Augest "Best Graphics Cards For The Money" paints them as being more powerful than a single 580), but this would mean if I came across a game that wasn't supported by SLI I would be worse-off than my single 570.
Since your first gpu is an intake why not put that on where a blower fan would normally be blocked with your intake, and placing the blower where it has access to cool air?
The only issue with that is there's only two positions for a gpu: very close to the bottom of the case or getting it's fan blocked by the other card. The first option is obviously better, but not perfect. As nforce4max said, a card that will exhaust is the best for SLI, since it pulls air along the length of the card from the back to the front instead of from the side (which will be blocked in SLI).