I can only speak on the 6600. I have had my machine for 5 years now and LOVE LOVE LOVE it. I have had several machines in the past but the 6600 is by far my favourite machine. I love the harp space, needle up-down, accu-feed, scissors. I have quilted queen size quilts on this machine and they were so easy to work on with the larger harp. This is one purchase you will never regret making.