Despite my hopes of spacing out my potential crossfire configuration between slot 1 and slot 3 to increase airflow between cards, I am bound to slot 1 and 2...but is that a bad thing? Does anyone know of any dangers or concerns of tightly stacked crossfire configs? The bridge my Asus Matrix 5870 is packaged with seems to suggest this is the only way to stack it given it's relatively short length.
I have really good airflow and cooling in my case otherwise (CM Sniper with front/side/bottom 240mm intakes and chimney ceiling 240mm and rear 120mm exhaust).
That is the most common spacing of dual video cards. If you get a space or more between the cards, you are lucky. I personally ONLY buy motherboards that allow a space between two dual slot cards. You will be fine.
It's possible the back of those cards serves as an intake. But anyway, it will be hotter but it won't break the card. You might try wedging something like a little folded paper or cardboard just to allow a few millimeteres of space for air to get sucked in.
It's pretty common for SLI or CF cards to be that squished.