Morrowind runs as fast in 1024x768 / Quincunx as it does in 800x600 / no FSAA on my system. I have a P3 800 / Gf4 ti4200. It is definately CPU limited for me. It runs ok, but frame rate dies when I enable shadows.... this is scary, because if my PC can't handle realtime shadows on a few characters, it doesn't stand a chance at running Doom 3 where the whole scene generates realtime shadows.
BTW, the pixel shaded water effect is cool, but it doesn't always accurately reflect the scenery around it.