I got a mATX AsRock z77 extreme 4
I was planning on keeping it with one graphics card (MSI 660ti). But the graphics card I got was DOA.
I couldn't wait and bought a new ASUS 660ti and RMA'd the first. It came back working (sent in the anti static bag outside the protective mouse and box - can u believe it lol!!)
You can see the problem with a mATX and SLI config, both gfx cards are so crammed together, the hot air from the first GPU blows against the back of the second.
What I did was put the ASUS in the crammed position. it is 20% cooler then the MSI. But at full stress the max temps on the ASUS are 80°C on the second MSI it's 64°C. Ok these cards are designed to work at those temps, but I don't like that. Ambient temps in winter are around 10 - 15°C. In Summer this will become a problem.
I don't know what I can do to lower the temps on the ASUS card, Is there something like a single GPU water cooling solution? or a remedy to get the airflow going between the two cards? or...
Does your case have side fans to blow onto the graphic cards? I'm also surprised that the ASUS is 20% cooler than your MSI. I got two MSIs myself for their aftermarket cooling which really makes it nice. My temps are 64/73 when both are going full bore which is fine by me. 80 isn't bad...just keep the AC running in the summer! Or another ghetto method is to remove the side panel and use a small fan and blow on the cards.
Water cooling is also an option. You can get an Asus water block. Just make sure your case has the holes for the radiator tubes.
when asus says its 20% cooler, it means that they are comparing the junk reference card to their card
SLI on matx boards are usually not recommended as cards like yours get crammed right next to each other. when you are going to SLI cards on matx boards, they are often the blower type designs (evga ftw is a good one for that) as blower fans suck air in and blow the heat right now
a side fan should help to get air between the cards
Slot spacing is important when it comes to thermal performance in SLI setups. Quite simply the cards are too close together, and the ASUS is being choked for air.
Might want to consider an ATX size board, or selling those cards off for a stronger single card.
If theres a grill down there, flip the PSU around.