Some time ago, I experimented with scsi and 15k drives.
They worked, but really it was not worth the hassle. I noticed no improved performance.
The value of 15k is shorter random access times, which is good for the os. It has no effect on data transfer rates.
Modern sata drives will be better for the desktop user, and if you really want performance, get a SSD.
You might get $150 for them on e-bay.