Well, I had basically given up and was getting on with building my new machine and I’d go from there . . . but . .
For the heck of it I tried turning off Graphics Acceleration for Cubase 8 with the Registry hack detailed here:
I did it ONLY for Cubase 8 - no plugins.
It seems to have worked. No random spikes. Performance seems OK.
Hard to tell if it’s “back to normal” because it’s been a while since I’ve seen “normal”.
I have had this same setup (without the hack) through several versions of Cubase and have not had the issue before - so it IS 8.02 related.
Several people in that thread have asked/pointed out that GPU acceleration SHOULD make things better - freeing up CPU time for other things - seems that way to me, too.
I am certainly NOT a programmer but it seems there must be something odd about the way Cubase is handling graphics that makes this hack necessary - and I certainly hope they clear it up VERY soon.
But for now I’m a bit happier.
Hugh