guys... just tried to put 4 7900 into on rig - failed. I use 1-16 powered risers, two PSU 1250 and 1000w. My win7 sees only 6 GPUs, one of them work on low memclock/gpu regardless of MSI afteburner settings. I tried various slots on my MB ASrock FM2A88X Extreme6+ - same results. Any ideas?