I would be careful about this one since the ASUS cards have a backplate. Naturally, you would think that the second card should fit if there's a two slot gap in between the two.I was just wondering would two Asus DirectCU II GTX 680's fit on a regular ATX motherboard? They should right?
I tried putting a ASUS Xonar Essence in the fifth slot of my MSI P67A (my ASUS DCUII GTX570 is in the second slot) and finally gave up and put it in the first slot instead. The video card, being heavy as hell sags downward a bit and I just wasn't comfortable with how much I had to jam the Xonar in there.
Basically, the topmost ASUS video card is going to end up touching the lower one, is what I think will happen. I don't think I've seen a picture of someone with SLI ASUS DCU cards. But there is a two-slot ASUS DCUII GTX680 curiously (it's lower clocked but has 4GB of VRAM).