Thanks for trying that Robin. For general veiwport perfomance, make sure that the display mode settings in Rhino 6 match what is being used in Rhino 5 as that version couldn’t do the same things in the display.
I’d agree with John B. that having you test 6.17 when you can is the best way to see if things have improved on a Mac like yours. My only other suggestions regarding what is slow still without trying to run an external monitor, would be to check that the named views are not using Raytraced or Rendered modes as those will take more system resources. If you do use Rendered mode in any of them, make sure the settings are the same as those in Rhino 5 for a better comparison.
If you can post any small file that takes longer to copy and paste from Rhino 6 than it did from Rhino 5, please do so. I’ll need to reproduce that here for a bug report. Please indicate the exact steps such as if you are pasting to/from Rhino 5 or Rhino 6 and what objects are being selected.
Raytraced uses a lot of system resources and was not available in Rhino 5 as you know. I can see that causing a delay on a system like yours which would only be able to utilize the CPU. The model size, lighting and materials as well as whether you are in a maximized view are also factors.
Waiting for ‘revert changes’ would be another one I’d want to see a file and specific steps for if possible. I’d need to reproduce it here for a report knowing exactly what was done in the file before deciding to close and revert those changes. One idea is to also check if the file was opened off of a network or cloud storage drive as that would be a factor too in any latency.