I played with the Babylock sit-down quilter recently too, and like Judi, I really hated their solution for stitch regulation. It's this separate mouse-like thing that attaches to the quilt sandwich and slides around on the table and that's how the machine knows how fast you're going. But if you get a roll in your quilt it's not detecting your movements anymore, and you have to keep removing and re-attaching the regulator as you work. Bleh! (Maybe they have other machines with better stitch regulators but I really disliked this style. The machine itself seemed pretty nice though.)
I really admire Leah Day and I have a Janome 6600 which is only a little smaller than the 7700 she uses...I **can** FMQ a king-size quilt on my machine but it is NOT easy. Leah makes it look easy, but she's a lot more skilled than I am! A LOT more skilled.
I'm actually about to start researching these large sit-down machines because I'm considering buying one later this year; I don't really know anything about them yet except that there are a LOT of different manufacturers making them. I definitely want one with a GOOD stitch regulator, that's a big part of why I want this type of machine. That, and the much larger throat.