The largest quilt I have done was the green and white quilt I made for my DS and DDIL as a wedding gift. It was 106" square and (silly me) I used extra high loft poly batting! The very center of the quilt was a little hard to manage. I just had to go slow and take time to move it when needed. Once you get the very center done, it's not bad at all!
Here is a picture of the quilt.