Hard disk drives have different characteristics, physically how large they are, how fast the platters spin, the method of data transfer, and the speed of data transfer. HDD's today spin at 5400, 7200, 10,000, rarely 15,000 RPM. I think that is what you are asking about the 7200 "ram" drive. Essentially all are SATA, and most transfer data at 3 Gb/s (ver 2.0) or recently 6Gb/s (ver 3.0)
The WD raptor is more an enterprise drive which spins at 10,000 RPM transfer rate 3Gb/s or 6Gb/s. The WD 1002FAEX is a high performance 1 TB size, transfer rate at 6Gb/s spinning at 7200 RPM.
For your new computer, I'd buy the WD Caviar 1002FAEX $89 at NewEgg, which will best match your i-5 760 CPU. Great hard disk.