The 6600 is a great machine, but just remember there is no freearm on that machine. It does have the Acufeed system though (a built in walking foot).
If you have the cash I'd go with the Horizon 7700 it has more throat space than the 6600, 11 inches I think. I love it and it also has the Acufeed system. The Horizon goes for around $2,600.