I have the 7700 and love it but have never had the 6600 so can't compare. I'm intrigued by the separate bobbin winder though (never had that either). How on earth do you concentrate on sewing while a bobbin is winding?? I know I'd have to stop sewing so I could concentrate on winding the bobbin so I don't think I'd see/get the benefit of being able to sew and wind a bobbin at the same time...lol. Besides, it doesn't take that long.