velociraptors have the same cache and RPM as old raptors, but they're overall faster, consume less power, and quieter, and does not put out as much heat compared to regular raptors. this is mainly because of newer technology and denser platters, so they're able to fit them in a 2.5" form factor instead of the normal 3.5". here's a few benchmarks of normal raptors compared to my own data on the VR's:
regular raptors in single
regular raptor in 2x RAID-0
velociraptor in single
velociraptor in 2x RAID-0