You can still build some extremely fast RAID0 drives thats still score a WEI of 5.9 or thereabouts - in my experience a WEI score doesn't really reflect the power of a good RAID0 setup. For example, I have 4 x 15,000RPM Seagate Cheetah SAS drives in a RAID0 that flogs IO speeds, yet still scores a WEI = 5.9.
I would agree that RAID0 drives are laregly redundant in a typical home-setup : they are still very handy in some specialist cases. When building a RAID0 the recommended setup is two disks of the same type. I wouldn't build a RAID0 with the Velociraptor and Hitachi.
Keep the Velocirator as a single drive, and reformat and keep the Hitachi as a separate storage drive.