Half running Einstein gravity waves and the other half running Seti work.
The two Ryzen's are running Seti and the two i3's are running Einstein gravity waves.
All running Einstein BRP4 work.
I finished reconfiguring the Pis. There are now 10 Pi3's crunching and one more provides support. Five of the crunchers have a 40mm fan bolted on top of their case for cooling. The other five have a desk fan to provide air flow.
I installed Debian Stretch a number of times during the week to see how things go. I had to reinstall once after the machine I was upgrading from Jessie triggered the screen saver and wouldn't come back. A subsequent reinstall moving the mouse every 5 minutes worked fine.
I also found out the hard way that rc.local doesn't run any more as one of my start-up scripts wasn't getting run. I ended up having to define a service to run it. I also had to set execute permissions on the script and service otherwise they don't run. They used to work fine under Jessie.
I tried upgrading one of the Intel GPU machines however when I logon instead of getting a desktop there is just the wallpaper and a mouse pointer. No icons, no taskbar and no menu bar. I tried reinstalling it twice with the same result so I've raised a Debian bug for that one.
I clean-installed the Nvidia GPU machines. They are all running Stretch now. If you are clean-installing be aware the enumeration of network ports is changed, they are no longer called eth0, eth1 any more.