Have you ever done Xfire or SLI setups before?
That's completely normal, one card heats the other. You wonder why people use raisers and place cards further apart?
You could rig a fan between but even that with 24/7 mining won't be too effective. If you plan on cramming 3 cards, 2 of them will run hot unless you decide to watercool.
80C is not that bad honestly, put all three cards in and mine for a hour and report back with temps you can always rig a fan on top of the cards to help dissipate heat.
Thanks !
You got me ! I'm a SLI virgin

As a matter of fact, I haven't had this chance so far... because I'm a Mac user (where there was no SLI support so far)
But I already had up to 2 GPU inside my Mac Pro to run on multiple screens, and never had since so intense issue/difference.
Yes, I have seen those awesome rigs people are mounting on open air, but I thought it was because they were putting 5, 6, 8 cards on such a small place.
Plus I thought that with a 3 huge fan chassis that wouldn't be a problem to host only 3.
80C is not that bad, I agree, but it's because it has been underclocked a lot (850Mhz instead of 1050Mhz), but at normal speed I'm around 100C (after 10/20 minutes) and I feel like the card is about to die with that horrible noise.
Question : Is MSI a good brand ? Should I go any other one ? Is it the way the fans are made maybe, should I go instead with those "reference cards" (you know the ones with the turbine and rear extraction of the heat) ?
I recently bought 3 Sapphire Toxic's from a group buy here, + 1 MSI in local shop, and I have to say that MSI is a "little bit" worse: