I have played with one of the Tiara machines (pretty sure it was a III) in a table about 6 months ago and I liked it. I couldn't get past the stitch regulator though, it seemed so clunky. But that seems to be how most sit-down LA's do stitch regulation, so unless I want to pony up $12K for the Q20 I might just have to learn to live with it or just do without.
That was really my only complaint about the machine though. Nice smooth stitches, seemed pretty easy to use, lots of throat space, decent looking table. I didn't try to thread it, though, mostly was just playing with it. That's going to be something I want to make sure is easy when I'm shopping more seriously. I also can't remember what bobbin size it had.