I've been able to mount backing that is 130" on my table (12' HQ) and still have enough room to deal with the machine. However the quilt itself was closer to 120". It did not matter that I had the backing closer to the ends than the machine would go as I wasn't going to quilt on the extended backing.
I started out with a 10' Grace frame (different setup) and quickly realized that was going to cause me grief on a regular basis - so I moved it to my dining room and set it up 12'. Now I've got the HQ set up in another building.