I don't know but I have two 10k's for boot and scatch and two 7200 1T's for internal data and back-up and a 1T external for bkup.
On boot: The new WD 10K Velociraptor Sata2 (about $300 each) single or dual drive boot time was essentially the same as the new dual platter WD 640G 7K Caviar (less than $100 each) in a test at Barefeats: [a href=\"http://www.barefeats.com/hard103.html]http://www.barefeats.com/hard103.html[/url]. Personally, I don't think you'll gain a lot by going with the 10K except a lighter wallet due to ti being about 6x the cost per gig. Also keep in mind it is a 2.5" drive in a 3.5" form factor sled, and a 3.5" drive spinning at 7200 RPM has almost identical outer edge rotational speed as the 2.5" drive spinning at 10K... Finally, the 10K VR is NOT standard SATA connector location, so is not compatible with the Mac slide in trays unless you purchase an adapter sled for another $50: http://www.maxupgrades.com/istore/index.cf...&product_id=180
On CS Scratch: Here you will likely see a slight performance boost, probably on the order of 10% or so over the 7K drive. However, I software striped (RAID 0) a pair of the WD 640's through OSX and gained about a 40% speed boost on scratch performance with CS, so probably a better place to spend your money. And of course you'll have 1.2TB of fast (but less reliable) storage after doing that. FWIW I partitioned off a thin stripe dedicated to scratch, and use the rest for working image storage since the I/O is about 2x as fast as a single drive. HOWEVERBUT, if you striped a pair of the 10K VR's it would probably smoke
Regardless, for maximum performance you do NOT want your OS page and CS scratch partitions on the same physical drives or RAID sets as they'll bog down competing for I/O time...
(Discussed this and some other MacPro performance tips in a bit more detail on this thread if you're interested: http://forum.getdpi.com/forum/showthread.php?t=2440