I wouldnt buy a p55 yet, not atleast till the foxconn stuff dies down. I was going to by an i7 860 setup a week ago, but after reading about the issues and not wanting to take a chance I just put the extra 50 bucks and bought an i7 920/mobo/ram.
Your power supply is designed for systems with 3 graphics cards and your motherboard is designed for one. Either drop the PSU down to a 750TX and get the P7P55D Pro OR drop the PSU to a 650TX. You cant 3way SLI/crossfire on a p55 motherboard, they dont have enough pcie channels.
At the $2000 dollar price point for a CAD system you really should get an x58 motherboard that is expandable to two graphics cards at x16 and an i7 920 CPU with a 750TX PSU.