6 Degrees for 1 more card in your system is not a big deal matey. Just keep that in mind.
As for more fans, you want to push all the air you can into the case, and pull out the 1 rear exhaust. Those cards are the same as mine regarding the reference fan layout. If they aren't reference cards and they aren't pushing hot air into your case - you want as much of the outside air to push into your case, over the boards as possible.
By the way, My AMD processor is overclocked and I use a Silver Arrow. - Excellent cooler.
That and the Noctua are the kings of air cooling for CPU'S. My CPU never hits over 50. It's usually far under even while stressed.
And with 2 6970's in the system in crossfire.
So don't worry.
...also did I say buy a Silver Arrow yet? *cough*.Edited by Eerazer - 10/18/11 at 1:16pm