they perform really well.
they've all got super low latency ram, and osx has used a prefetching system long before vista came out, so everything feels like a smoothly integrated program, with much less loading time between launching programs compared to windows.
the only acception i'd mention is the video editing program, which is obviously huge.
prefetching cuts down on peak application speed, compared to windows, but i guess that's just the tradeoff for a smoothly flowing multitasking experience