I'm also looking for 1600w PSUs, preferably Lepa or any other silver/gold efficiency.
So you're looking to build 2 GPU rigs with 5 280x each? Each rig will pull ~1600W (maybe a lil less?)?
Why not buy 4x 800W PSUs? Each rig can use 2 800W PSUs, One for the MB and 2 cards, an the other for the last 3 cards. Works quite well, and saves you some cash! Those 1600W PSUs can be expensive!
That's correct, I want to add roughly 9mh/s to my current setup.
As for the separate PSUs, I've seen it done before, but finding a few gold rated PSUs (from what I've seen) normally costs more than a single PSU.