I have a box with OC'ed XP1600+ running at 1.585 GHz that consistently runs a HAR WU in 2h56m. The overall average per SetiQueue is 3h20m.
When I had WinXP Pro on this box the best time was 2h59m, but I went back to Win98SE and the time improved by 3 mins. But I got much better times with 3D Mark 2001 under WinXP Pro. With Geforce3 Ti200 I got a score of 6833 3D Marks, but with Win98SE it dropped to 5997. With both configurations I was using Det. 23.11 drivers.