Welcome to the board from Southern California!!
I have a 630. Had been looking at the 640 but had a lot of people tell me that if I mainly use it for quilting that it is harder to maintain a 1/4" seam with the wider feed dogs.
I know that you can just move the needle but I like using the 1/4" foot to sew with. I have the BSR and an embroidery module. Love my machine!