Stats are not everything when it comes to sound quality.
I have read on different forums that people like the VX-10 better than the STF-1 so it really is purely subjective and dependent on the room and acoustic environment in which the sub is used. I have not heard the STF-1 so I can't really argue my opinion on the two.
If the STF-1 is better I would argue it is only marginally better and the OP would be better off getting a substantial upgrade over the VX-10.
HSU makes great subs, but so does Velodyne