I have the 6500 because at the time of purchase I could not justify the difference in cost to go to the 6600. I love my machine just wish it had the few extra decorative stitches that are on the 6600 ... again not worth the price increase for stitches, LOL
The 6500 is great for quilting, I love the extra throat space, needle up/down and all the other features including auto thread cutter.
Since I don't have the accufoot that comes with the 6600 I have no comparison to make.