The Velociraptor is very nice and I don't know much about the Savvio, but I would actually get the WD6400AAKS
and at least try it out. It's only $85.00 and is a pretty fast drive.
I have a 74G Raptor HD and have installed a few 150G Raptor X HDs. I was really impressed by this drive. It certainly doesn't have the seek times of the other drives, but you might be pleasantly surprised by its performance. If your not, then use it as a fast storage drive.