NT up to 3.51 was slower. Then they moved the GUI code into the kernel space and it picked up pace dramatically. I think I still prefer the GUI code in userland though and I can't say the speed bothers me. Window redraw on my X, particularly if I'm moving a widow in front of another, is visible (on Windows it's not), but not to any extent that I would consider it a hinderance or even slightly annoying.

Besides, KDE and Gnome are just bloat IMO. I use just WindowMaker with no desktop environment and run just fine (and blazing fast). GUIs are overrated. :-)
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Makeshifts last the longest.