Hi,
I put together the small version viking megaquilter with the gracie next generation frame.
The viking is about the same as the janome 1600, just different plastic on the front, I think made by the same company.
The next generation frame is 4 rails, 120" (ten feet) long.
I made leaders to total 115 inches. That should hold a queen size quilt.
Your question about length is to turn the long side of your quilt left to right so you don't put so many layers of rolled quilt into the machine throat.
I can comfortably quilt up to 105 inches left to right, because the bunjee cord tension clamps on the right and left sides of my quilt back bump into the machine carriage when I get to within 3-5 inches of the edge.
If I have to sneak another inch or two, I unclamp the edge when I get really close and drive with one hand while steadying the quilt edge with the other.
Not the best, but cheaper than the alternative.
So far, I really like my machine frame and machine.
Keep shopping and comparing features!
Give me a shout if you think I might be of any help.