I also have the 6600 and love it! The Acufeed is fantastic and I use it even for regular piecing - for eg if sewing long strips, you don't get the bend and bow at all! And for FMQ it's also fabulous - I prefer a gliding foot rather than a hopping one so bought the optional foot and the blue dot bobbin case which helps with tension. I was lucky that a friend had the machine so was able to have a go on hers first before committing to it. I got mine just over a year ago and shortly before the Horizon came out - I could upgrade but manage fine on the 9" throat. I'm currently quilting a 70" x 54" quilt on it, no problems.