I have the Janome MC6600P and love it. It has the same size harp as the Horizon just not as computerized. It does have a thread cutter. The Horizon and 6600 have the same accufeed system.
I love my 6600 because it is not a very computerized machine. If I need to move the handwheel to have my needle land exactly where I need it, I can do that without harm to the machine.
I've had my 6600 for about 4 years now and have yet to take it in for service. It runs like a champ!