You can do a queen size quilt on a machine smaller than the 7700, but it isn't as fun...
The 7700 was $3000 when I looked at it. I've heard it is about $2000 now. If it was that when I was looking, I'd own one for sure. I LOVE the machine I got- but the harp space is amazing, and its features are really nice. I don't like that the 6600 doesn't have a freearm, that is a must for me. I did have problems with the 7700 going through many layers of denim- I had to slow down my stitching, my current machine will do it at full speed without blinking...