well, in my case I chose to make the footbox close up around my feet completely. The pic shows how it will envelope you feet and lower legs, and you can almost see the hole left (where the sock will go)
what I was talking about doing is placing a few snaps at the footbox area to avoid itchy, sock grabbing velcro.
yeah, with a size 13 you'd need a bigger quilt... I also made the 45° at something like 50x40x78. It has a sewn thru baffle with 6 oz down and weighs 12.3 oz. I actually used it this summer at 9200' and with just nylon pants, and a poly t-shirt slept down to 40. Feet were slightly chilly come early morning but I could have saved them with a beanie, which I did not wear.