I just added a second 5830 to my rig.
The temp of the 2nd card is in the 75-85 range depending on the fan speed and my overclock.
The 1st card is in the 55-65 range.
What temperatures are your hottest cards running?
How long have you run them that way 24/7?
I tend to think that in the 80's is getting too hot, what do you guys think?
80 is the uncomfortable point and I try to keep mine around 70 as much as possible.
First, my case doesn't support the airflow that it needs so I leave the panel off.
If you have to keep them side by side, space them out as much as possible, I left the screws off and stuck a molex (4 pin power connector) between them to open the spacing.
I put a 120 mm case fan over the cards to push air from outside the case down between the cards so the fans are getting more fresh air as their input.