I added code to trim my supply and the good news is that it looks like the board is stable at 35GH/s at 0.975V. To get any faster than that I need to get over the max 1.050V my supply is able to put out (to do that I need to disassemble the cooling and change a sense resistor - not terrible but it is a hassle).

A single chip (the board has four) almost works at 1.050V/40GH/s. If I run all four then the supply under load drops to about 1.030V which doesn't work too well.

Need to validate this on more than one board of course