Thanks lastbit and GandalfG for the info.   I have access to a nice 12ghz oscilloscope and will take noise and ripple measurements of the output of the VR and see if it gets unstable past 20a.  

I am running a 1200w supply so I should be fine on the supply side. Going to be switching to 220v as well to gain a bit more efficiency.

I will be running coolant to a radiator outside for watercooling...  Unfortunately it has been 105f or 40c for the last month outside.  Which is even more reason I want to get the 800+watt this thing produces out of my house!

The main issue I see with cooling is getting the heat from the chips into the heatsink.  lastbit's photo earlier show the exact bowing away Im seeing.
As the board heats up you can watch it bow away.   I have a clamping solution im working on as well to hold the chips flat against the heatsink.
 

Just took some measurements.  At the top of the board closest to the VR im seeing 1.2v at the bottom im seeing 1.15v!  Im surprised to see so much of a drop!  They must have cheeped out on the amount of copper on the board.