Toby,
I haven't played the superfilter bass, but after some deep thought on the subject, that bass probably isn't the right one for me-there's just too much going on with it electronically, and the fact that it needs some neck work to be fully playable is a bit of a turnoff. I'd have to revamp my rig to make using it practical.
Unless I'm offered a great price on the superfilter bass, the Series I is probably my best bet right now.