I am working on a king size right now.
I am tying it on the sides and the bottom. The middle I am tying it from the back cause I don't want the ties in the block designs. When I started tying it, I didn't think about the little ties sitting inside my blocks. So, mine will be about 1/2 tied from the top and 1/2 tied from the bottom.
Also, you actually have a 3rd choice on finishing it. You said either birth it or bind it. I am going to make my own binding and bind mine. You could also make the backing about 4-5 inches larger all around and fold it over to the front and pin it down and then sew it down with the machine. We just did one like that at the Guild and it turned out really nice.

Hugs,