The main reason why server-side stuff is slow is poor use of the database. Doing e.g. nested loops in a compiled language uses way less CPU than a scripting language, but it should be done in the DB in the first place.
I used XMonad for about 1 year. Back at FVWM since ca. 8 years, but XMonad influenced the setup quite a bit. The WM is barely noticeable, it manages 2 full screen rxvt/ssh/screen windows, Firefox, Zoom and little else. Keybindings + integration with a self written Plan9 plumber-like tool (edit/modify selection, link to bug db, jira, ... based on selection contents) are the real productivity boosters.