No powered risers.Super stable build board ..optimal layout for mining which made it -and still makes- it very popular among miners.Need I say more ?
I run 3x5970 and one 5830 inside the same rig, using MSI GD65 motherboard, so with your logic it is actually 7 GPUs on the same motherboard, I tried to stick another 5830 in there, but that didn't work - windows just refuses to get those cards configured correctly.
I'm using 1200 Thermaltake PSU for entire rig, which was enough for entire setup with 1250 at the wall mining BTC.
Once I switched to LTC, the system just refused to stay up once GPU # 4 was switching to LTC from BTC, so I had to add another PSU at 620W.
2 smaller PSUs would be actually cheaper then a monster PSU at 1800 or 1650.