Some may disagree with this, but the first quilting class I took, the instructor told us that she used sheets for larger quilts. I have used sheets for backing a couple of times, but I was machine quilting them and they were for using, not show quilts. I think it's a matter of personal preference, however, I think the 400-500 thread count sheets would be more difficult to even machine quilt. That's my comment, do what you want and how the quilt will be used.