I bought a 7700 18 months ago and I love it. I had done no FMQ at all before that. Since then I have done numerous placemats and over 45 quilts. Most of those were baby-sized charity quilts, but the throat easily accomodated a queen-sized quilt.
I have used many different threads and all have worked once I found the correct tension setting.
Using the APC set to straight stitch (D1S) is crucial for FMQ. It is also important to set the hopping foot so that it is not too far above the quilt to prevent thread breakage.
The 7700 is not as good with thick fabric like hemming jeans as my Bernina 1130 was.