7200RPM SATA300 or 10000RPM SATA150

SATA 300 makes maybe a 0.00001% difference, and that is only because you can read/write to the drive cache faster.

10k RPM on the other hand makes (imho) a big difference, The WD Raptors are excellent drives.

The advantage of SATA300 lies in the use of port multipliers and solid state drives.

SATA 300 interface looks good on paper, as darkstar782 pointed out, but Western Digital doesn't even use it on Raptors, because HDD's still don't use the bandwidth of SATA 150. Purchasing a hard drive should not be based upon SATA 300 / 150 interface. Check out the following THG articles:

http://www.tomshardware.com/2006/02/06/wd1500ad_raptor_...

http://www.tomshardware.com/2006/11/27/15-years-of-hard...

Hope that helps. Enjoy!