Are you planning to do piecing and quilting? Do you need fancy stitches or just straight stitches? Are you planning to use a machine for the frame and for piecing?
There is a mechanical machine that only does straight stitch. It's available by Juki (I think the 980), the Pfaff Grandquilter 1200, Brother has a version of it and so does Viking. It has a 9" throat and is often used on a frame.
I would not want to lug a machine on and off the frame.
Have you test-driven the Janome and the Bernina to see what you like? That would be a very strong indicator for me.
My new machine is a Babylock and it has a substantial throat too.
Aaaaaah, all those choices. Have you read the reviews on patternreview.com? They have lots of good user inputs.