Re: 180.60 & High CPU
OK, now I've found it. Option "DynamicTwinView" "False" and indeed now K|Settings|Peripherals|Display reports 60Hz. nvidia-settings still reports 59.88, which is OK.
Apparently xrandr cannot differentiate between meta-modes of the same size, so the nVidia driver lies about the refresh rate so it can differentiate. Thanks rapsure.
I am still left though with this CPU-hungry X. How to dissect what could be causing this is a Mystery To Science.