@Onebyone and
@mkc -- ditto on their advice. I bought a Pfaff Ambition 620 (one step down from the 630) and I really like the IDT. It helps with piecing. Unfortunately, it doesn't seem to like chain piecing. It tends to jam in between successive quilt blocks.I also like to applique, but I use the blanket stitch and not the satin stitch, the Pfaff works great. I don't think the throat size would be big enough to FMQ anything bigger than a twin. On one of the other posts recommended using a pool noodle as a guide for using a long arm frame on a DSM to see how much throat space was available when the quilt is rolled up. Maybe you could apply this to your shopping?
I like to shop for machines at the quilt/sewing shows, plus you get good deals. Also check the Pfaff website for monthly deals. I got a free extension table when I bought mine.
Good luck on finding a new (or two) machines!