And I don't buy Tony's point about fragmentation, either -- Windows comes with a perfectly functional defrag program.

Fair enough, and maybe I'm offering up the wrong explanation with the fragmentation issue. It may have more to do with extra parallelism that can be had when multiple physical drives are involved (which is how my partitions are set up) so I'm getting sort of a "poor man's RAID striping" effect. Whatever it is, my experience has shown that, regardless of the speed of the drives involved, I've had better results with multiple "specialized" partitions. YMMV, as always.