I specifically just bought an old industrial Singer 31-15 for fm quilting because of the larger harp space. It's a BEAST of a machine (I'm told the head weighs like 65 pounds!), but the harp space is like 11". It has a vertical bobbin (which is desirable for fm quilting because of the thread path), and does beautiful quilting.

I've just finished up free-motion-ing a queen-sized quilt on a Singer 15-88 treadle, which is a 'normal' harp size of a normal machine. I was able to do it, but it was like trying to wrestle an alligator!

I did win in the end. :)

thanks for all the helpful hints and info on long arm quilters....it will definitely be something I want in the future (but will be lots of saved pennies later)....I will try again and see if the result is better.