Håkan,
A while ago, I made a (theoretical) burst performance analysis of a couple of harddrives. I now added the Caviar Green as well. As you can see from the table, SSDs are clearly superior to regular drives. The Caviar Green doesn't stand up very well in this competition. Even though regular drives can stream a reasonable amount of voices when triggered sequentially (such as dragging your forearm on the piano), they are terrible at pure burst performance, triggering many notes at once. Quantized music would be the hardest task for a mechanical drive.
Many new libraries, such as Dimension Strings or Hollywood Strings, trigger many voices (players, microphones etc) exactly at the same time. Then the burst values from this table are most important.