Anyhoot, that motherboard is an MSI motherboard that was made specifically for Dell. It has 3x x16 slots, and 2x x1 slots. You can find them on ebay for like $50 to $75. "Dell 730x motherboard" Make sure they are not "Dell 730" <- that "X" in the 730X means X58 INtel chipset. A "non-X" means NForce LGA775 socket!
A virgin copy of LTCRabbit freshed minted onto an USB, booted, and BAM - all 5 GPUs mining away (no tweaks yet).
I really want to believe this mobo can be had for 50 to 75 on ebay, but a search for sold or completed listing using "Dell 730x motherboard" returns items that were sold for $120-$300 going back to November. Anything in the $50 range is nothing more than a mobo tray. Like I said, I WANT to believe this to be true, as I would gobble up some boards. But it just doesn't seem to be the case on ebay right now...
how long ago did you grab the mobo?