I had the 6500 for many years and loved it -- it served me very well for many years and now DD has it and loves it too. I was really bummed, however, because I bought the 6500 about 3 months before the 6600 came out and I really wanted the accufeed. I tried it out but I could not justify it so soon after buying the 6500, but started saving just the same.
Just about had enough money when the 7700 came out, DH tossed in some more money for Mother's Day and my birthday and I got the 7700. I use the accufeed for almost everything -- I love it!! I don't know how I lived without it.