I run 8 of the same sapphire 5830s oced to 950 and with fans at 80% they run at about 90-95 degrees on a hot day in my garage. Except for the cards on the end of the mobo that get fresh air. I run 2 high cfm 120mm fans setting directly on top of the cards and don't even bother with a case.  They key is to make sure all of your mining gear is going in a room you can't hear or feel the heat from.