I just did some tests for some common things in my workflow.
I couldn't find any speed difference when using a 1tb seagate 7200.11(new and unused) vs the 500gb seagate 7200.10 boot drive that came with my computer. I saw that at the scratch disk was getting used (about 4-6gb worth on each test). I thought I'd see a faster result from using the 7200.11.
I did find something interesting though. When I ran picture packages or a batch action on 25 files, they ran almost twice as fast if I clicked back to activity monitor or safari or any other program. If I stayed in Photoshop and watched the action run it took way longer. ie. 25 picture packages took 3min15sec to run if I stayed in photoshop but they only took 1min45sec to run if I clicked over to another application. I could even be doing something in another application and they would run faster. Weird huh?
The only thing I can think of is that the photoshop is trying harder to produce the image for you to see if you don't click away. Maybe the graphics card slows things down (I got the stock ATI HD 2600)?
I was borrowing the 7200.11 for scratch (it's really meant for backup). And, I still feel I need a dedicated scratch disk so that my other disks remain less fragmented and more pristine. I really wish I knew if the raptor and/or raid would be faster for me (by the way, my processors never went above 15% for these tests so software raid 0 should speed things up right?).
Anyway, it's nice to know a trick that doubles the speed of what I do for free!