Yes, I kept the Quadro P2000 as the renderer.
With Open CL OFF it is responsive at the beginning but become buggy and slow when editing panoramas (100mpix and more), pictures with more than five or six layers, or when doing frequency separation and using the mixer brush. The brushes, toggling the visibility of layers, switching to another tool become slower.
But the most annoying issues are the freezes, it's like a sleep behavior, where the mouse pointer stay with the brush preview when I'm trying to select another layer, tool, or the assistant robot icon. Going in another app to come back in AP2 seem to wake it up, but frequently it become completely unresponsive and I have to force close it.
But maybe I have just found a solution, I disabled Windows Ink in wacom app and it looks like it make a difference in the software. Can't be sure yet because I'm just trying with few layers, I have to try it in a real case scenario. Settings are: Windows Ink in wacom app untick; Pref/Performance Quadro P2000 as the renderer, retina on auto, Open CL Off; Pref/Tools "High precision". I will investigate further the software with these settings, if it's working like a charm I will know there is a conflict with Windows Ink in wacom software.
Thanks for this information. If the new settings are not working well I will open a new thread.
Thanks again @SrPx for your help.