One thing I highly recommend, since you are researching so thoroughly, is to join the free yahoo groups related to each machine model. I belong to the Janome Horizon group (7700, 8200, and 8900) and several Bernina groups including the 7 series group. Reading those made me a little wary of the 7700 and the original 7 series (710, 750, and 780). It seems in both cases, the successive models (Janome 8200 and 8900 and Bernina 740, 770, and 790) solved issues with *some* of the initial models. I follow both closely, reading the digest daily. I wouldn't hesitate to buy either an 8900 or 740/770/790 now, if I were still in the market. I would be a bit more inclined toward Bernina, because I have and LOVE other Berninas, but I think the 8900 is also a fine machine and usually costs less.
Nothing at all against Baby Lock (or Brother), just that the current offerings are don't excite me. I have a Baby Lock Quest Plus I also adore, and it was a small fraction of the price of Bernina models with similar features, and about 1/3 the price of the Horizon 7700, which was rather similar. Unfortunately, Baby Lock doesn't have anything like that model now.
The Bernina 7 series are very heavy, 30 lbs or more. Mostly a problem when you are taking the new owner classes, but maybe the dealer has a solution for that, like letting you use a floor model for the classes. Other than that there's repairs and routine service. I have several Berninas, almost all bought used, and none has needed anything but routine service, and I don't even do that yearly, since my sewing is spread out over a few machines at least.
Best of luck in your search and purchase!