"I did not expect much, and because the bottlenecks were the HDD and CPU I did not feel any noticeable performance improvement."

Sounds like it started on XP running poorly, and ended on Arch... running poorly.

twm still around but might be a separate package these days and not in X11 core. CWM (Calm Window Manager) from OpenBSD is available in portable form and packaged for Debian. Very light and good for tiny screens (little decoration).

would love to see twm get active again as well