I currently have 2x 200gb 7200rpm drives on my desktop.

As always, i want it all to go a bit faster:

Is it worth getting a 15000rpm scsi or a 10000rpm sata or just get a
mammoth 500gb drive (7200). I want to speed up boot time and make the
applications run a little faster.

If i decided to get a 36gb sata (10000rpm) and made it my OS and
application drive, would i notice a difference. Or is it worth getting
a 15000rpm scsi --> the specs look awesome, but would i see any
change???