Right, YOU CANT JUST PLUG 8 CARDS INTO THE MOTHERBOARD!!! The normal extenders supply 75 watts from the board. RUnning 4 VGA (4x75W(300W)) is the limit. Least i found. I blew a motherboard plugging 5 in it. YOu need moidify or buy extender WITH POWER MOLEX to power the cards direct from the PSU. THats why i kept my rigs below 4 and still use power molex for the 4th card as it loses performance without i found
Although i dont know what all your cards are. I run 5850's.
I hope you have VERY GOOD 1000W or GOOD 1200W, i.e, Corsair AX1200, antec HPC 1200W PSU's etc, I blew a cheap one and cheap one = KNACKERED HARDWARE, i warn you now
YOu thought about HEAT! i got 8 running now.well 11 with comp, and use a 12" out take fan to get rid of it. 2x4 rigs. Bottom pic on this post shows what i use for extraction of heat. its HOT! without something. https://bitcointalk.org/index.php?topic=18567.msg494839#msg494839
New (11.6+) drivers dont need DUMMY's at the back wither with windows (if your windows). Although 10.4 with 2.1SDK is the best. CGminer and diablo.
AND FANS, you need fans mate. serious fans, them cards are close, WAY too close if you ask me. In in for a suprise i recon haha. 2 rigs of 4 mate, 2 rigs of 4
Greedy, i tried