feels as you move it is so important, and again if you have any back/shoulder issues, this would be important to know how you feel about doing the motion for hours. you also lose about 5-6" of harp space due to the roller and quilt as you quilt more, so a smaller machine with a 16" harp will only allow you about 10" of quilting space. most quilt blocks are 12", so it's difficult to do a custom design inside a block without having to advance the quilt.
as others have mentioned, you should definitely try out as many as you can, and for as long as you can. i'm happy 