I am one of these persons that "if it ain't broke, don't fix it." For a large quilt, I love 12" blocks, so I got five across/seven down, 2-1/2" sash, 4" border. If I don't want the sashing, I add one more block up and down. For the coverlets, I use my 12" blocks - 3 across/5 down, same goes for the sashing. The coverlet ends up 52x80 and the large quilt is 80x104. That is with the 2-1/2" sash and 4" border. Those are the only two sizes I like to make. My baby quilts are the same size as a coverlet. I like them for on the floor, to go on a youth bed or t win bed.
That's what I do. Edie