I quilt all sizes on my Berninas - 630, 180 and even my 40 year old 807.
I guess I use a puddle and roll combo!
I also have the luxury of an 8 foot by 4 ft work table, for quilting big I clear off the table and spread the quilt out while I work.
I mark my really big quilts into 8 sections and just 'pretend' the 8th I'm working on is all the quilt! I also sit on a pile of cushions and I dont even look at the machine with out my gloves and three wound bobins.