Alright, so I am currently in the process of extending a personal mining pool that is in operation with two other friends.  I just received more Sapphire Radeon 5850s and plenty of Mobo, CPUs, Memory, PSUs etc to build out.  However, I am curious.  I was originally planning on operating only two cards in each machine, or perhaps three, but if I run 3 on the motherboard, I am worried about heat of one of the cards, because it will be directly next to another card.

New hardware:
http://s4.postimage.org/30tx7i6zo/photo_1.jpg

Additionally, I've thought about putting 4 to a machine. 

Motherboards are MSI K9A2 Platinum Motherboard

My question is, based on running them @ 850/900 @ 1.088v (stock voltage) which consumes in the neighborhood of 250W (give or take 20W) at full load, each.  Do you think the heat would be too much?  Currently all my 5850s are 2 to a box, at the cpu/memory and voltage previously mentioned; and operating at 60C - 62C without any issues.  Granted, they're running on a datacenter floor with plenty of cooling, so I'm not worried about the room temperature, it is already super cool ~ 64F.

This is the proposed configuration of four:
http://s2.postimage.org/26o1ijtyc/photo.jpg

Do you think it will be an issue?

All in all this will add another 3GH/s to our pool.  Which is always great!