With the new build downloaded on 5/28 the speed has dropped to 580MHz (with a total hash rate of about 1.9TH for the three R606). I'm going back to the earlier version since it works so much better on the Pi Zero. Probably if I ran on a full power PC with Windows or Linux the newer build would work better.
My data point is 700, 705, and 710 MHz on three R606s using Raspi Zero at voltage level 7 giving total 2.6TH on average after about 5 days running on build a62385f.
Still pleasantly shocked that Pi Zero can handle this!
I'm going to download the latest build tonight and start a new run to see the difference.