I have a 9" Janome on a New Joy frame. If you're only doing meandering or some other simple back-and-forth quilting, it's fine. But if you want to do designs inside blocks you may end up running into trouble with lack of space, and you may even have to take the quilt off the frame, turn it around, and reload it so you can finish.
I have lucked out with a recent acquisition of an 18" Wow (stretched Singer 201) and am currently expanding my frame to accommodate it. So excited!!!