I have two R606s running off a Delta 2400 supply that is also running an Avalon miner.  The two R606s are two serial numbers apart, but far apart on performance:
The low one is: 732,487.17 MH/s over a two day period
The high one is: 783,674.91 MH/s over the same two day period

I guess the difference is because the ASIC chips are not binned.  Really that is all that it could be, same PSU, same computer.
Incidentally thanks @DieselWeaseI !  I purchased an oDroid-N2 to run these R606s and some staking.  The oDroid-N2 really runs great using Ubuntu 18.04 mate.  It runs rings around a low-power celeron that I was using.

Forgot to mention both R606s are at voltage setting 4 and trying to run 575 MHz.  The lower one will not go much over 536 MHz, the high one runs all the way at 575/575/575.