I had a very stable 98SE system for a long while... I tried ME and 2k, but my fave game at the time (UTournament) ran slower in both... in fact ME was appalling in that respect.
I've just recently setup a dual 98SE/XP system, as JediKnightII totally froze my 98 setup after installing.
XP copes with JediKnightII admirably, despite me "only" having 256mb PC133 RAM (i run it at 1600x1200x32, everything but shadows maxed (which seems to slow keyboard input, but not gfx), on a tbird1466, o/c vanilla gf3).
XP can't cope very well with many older games or emulators though... some fail completely, painfully slow in some, no sound in others... 98SE is better in that respect.
I'm interested in finding out what 2kPro's like though if XP is seemingly so bloated.