I am not developer but i think i can say im computer literacy. I know difference between system hang/crash and cpu overload. I used many demos, eg 64k heavy demos from demoscene, furmark or other 'marks and none of them stalled my screen. Any of them i could shorter or longer kill from task manager.
While emu writes to rpsc.log, my screen hangs, always after at specific commands, which are in my first post. And system doesn't react on any input. I believe it is because GPU driver fault, not cpu overload. I did not encounter such behaviour with rpcs3 earlier. Look also on #906
https://github.com/DHrpcs3/rpcs3/issues/906 issue. I don't blame anyone, but i believe some late RSX code might behave wrong with some faulty(?) GPU drivers.