If your interested in a used machine, I know on the Yahoo Janome groups (6500, 6600 and the 7700,8900), folks advertise their machines for sale when they upgrade. I think it is the first two days of each month that folks are allowed to advertise.
Maybe the other machines your looking at have the same setup on Yahoo.

I bought a 7700 from a dealer not far from my home at a really great price but my second choice would have been the 6600. I believe this month they are having the Janome dealers convention where the new models will be shown. Perhaps prices will come down on the older models.

Whatever you choose, enjoy.