I love my 6600! I test-drove a 7700 and didn't see enough features I liked to upgrade from my 6600. Wow, I just can't imagine not liking that machine, I love mine so much! But of course, to each their own!
I have FMQ'd a 120" square king-size quilt on my 6600 and it wasn't too bad at all. For me, the 6600 is plenty big enough. I also have a Janome 3160 as my portable machine; both are absolutely lovely to sew on.
I don't do much embroidery; I have a relatively inexpensive Brother for that. (PE770, bought on Amazon)