The last version of Arc Capacity planning spreadsheet by Dave Paters was released in March 2019. When do we expect another version of the sheet with more workflows and hardware specs#CapacityPlanning
I can see that Dave Peters is now retired, not sure who is going to continue his work and update the tool
The CPT has not been updated in a very long time and is no longer maintained (to my knowledge).
I think the work of Dave Peters is continued by the Architecture Center team, but in different form.
In the Architecture Center, you can find reference systems: About test studies | ArcGIS Architecture Center
You can use the Architecture Center as a general reference. Then set up a test system and do Performance Engineering: Load Testing ArcGIS Enter... - Esri Community to adjust your infrastructure to the expected load. -> Design an effective test strategy | ArcGIS Architecture Center