So, I don't actually have the system yet, but i will get a CM 690 II Advanced case, and an overclocked 5850 (will overclock myself). eventually i'll get Xfire. my question, is, should the graphics card(s) be on the top 4 of the motherboard (near the north/southbridge) or near the bottom (near the CPU) and, in what direction do the GPU fans blow? I think the question more depends on the direction of the fans cuz that will determine what direction i'll install new fans...this answer maaaaaaaaaay or may not determine what motherboard i'll get.
The HD 5850 should be installed in the (or one of the) PCIe x16 slots on the motherboard. The first (or only) of these slots is usually under the northbridge heatsink, sometimes there is a short PCIe x4 slot immediately above the PCIe x16 slot. If there are more than one PCIe x16 slot, the second is usually under the first.
Most all, if not all, cards pull air up from the bottom, and out the back (PCI slot). See TGH $2000.00 SBM pics.
You won't see any difference b/t mobo. There are much the same. THe 1st PCI-e slot is x16, which is "top" slot. The "bottom" slot is only x4, or even x2. The card will work in them (I think), but you'll lose alot of speed in the high end card!
P.S. THe CPU is not on the bottom of the mobo, it's in the upper left hand quarter (is that above the southbrige chipset?). Look at some pictures of complete systems, you'll see the layouts. They'll probable answer your questions better than anything.
well, where i said "near the bottom (near the CPU)" i was actually saying near the bottom (near the PSU) because the CM 690 II Advanced PSU is actually located on the bottom. I will be getting an x58 motherboard because of the crossfire expandability.
i found a really great review site that emulates an HD 5870 in a PCIe x1, PCIe x4, PCIe x8, and PCIe x16 slot to compare speeds.