Re-read that. During gameplay, it can get to 50%. I am running Java 64 and minecraft server has been multi-core capable since 1.14.
Before optimizing java settings, it would get as high as 80 odd %.
I ran this setup on Ubuntu on an older Acer Aspire laptop with the 1.67ghz Intel Duo with only 4gb of ram and it screamed. I never saw the "server is behind xx ticks" message. I didn't have all the config flags running that I do in Windows and memory settings were 512 and 2048
Either there is something missing or the overhead of Win 10 is a bottleneck to achieving better performance.
Next up, my original question, are these parameters valid for server.jar?