Hi, I am performing the same tests if that helps!! Our use base is around 1000, where I would expect 200 concurrent sessions (I have already seen ~130). This is currently in a dev environment and i am planning production now. All this is running in Azure on a D16s_v3.
I would be interested to know what you are using for load testing. I have not found tools that accurately mimic load, but that is more to do with the makeup of my dashboard.
Overall for the last 6 weeks the performance has been good, however I still get random spikes of CPU to 100% (Unresponsive Dashboard 2.9.0) when some process is either performing a DoS or a lookup loop. I have not got to the bottom of this as yet (probably endpoint related). Another thing that has helped dramatically is using @psDevUK timeout, this stops a lot of errors on the dashboard.
I am also now looking into sticky sessions behind an Azure load balancer with 2 dashboards running HA, i have this working and its going into testing tomorrow.