Loes ...
As for the the 6600 not having the free arm, I did give pause to that; but I have my 43 yr. old Bernina if I need a free arm ... and I do have a grand baby on the way (girl ~ due July 26th), so I'm sure I will be using the Bernina if I need that feature.
Someone mentioned sewing on *light* fabrics. Well, one of the demos I was shown on the 4120, was sewing on Kleenex (tissue), and it sewed beautifully on this tissue. I couldn't believe it. Of course, this shop only sold Janome, so they did say it was pretty much a feature, only Janome could do. True or not ... but it was impressive (and NO puckers/wrinkles either).
As I said, I probably would have bought the 4120, but the shop I got it from does not do the *trade up within a year* program; and I know, IF I wanted to upgrade, it would not set well with my husband. He thought there was nothing wrong with me sewing on a machine 43 yrs. old .... and I finally told him: *hey, it's "almost" a half century old* .... and I think he got the picture!! lol
Again, I think the 4120 is just a great sewing machine and you could not go wrong with it .... or the Janome brand.
jody