It seems like you want two opposing things. You want a large harp for quilting (which means a larger, not portable machine) and you want portability. If I were you I think I'd take a long look around to see if there was a space somewhere where you could permanently keep a machine on a desk and give up the portability, maybe in a basement, spare bedroom, etc. Then you could buy the machine you really need and not worry about lugging it around every time you feel creative or have some time to quilt.