As it turns out, the Windows Notepad isn't really well-suited to act as a stable, consistent view window for a fast-paced game like Doom. Chiet's 60 fps demo has a lot of noticeable flickering ...

Newer professional pinball games are able to run ball logic internally at a ultra-fine granularity rate roughly equal to the gaming mouse pollrate (1000Hz) for this reason, for latency consistency.