first off you gotta tell me where you got APEX! I can't find a good reliable source for climashield anywhere right now.
For 5'10" i recommend a minimum of 74" quilt with the drawcord style footbox, but you would be happier with 6". However if you do a sewn in round footbox you can use the whole 72" and it should give you the coverage you need. The process to make a quilt with a sewn in footbox is different but still not too hard. I'd think you'd be good with a quilt 48" wide at the top and 38"-42" at the foot(depending if you want it to fit close or loose). I like my quilts to be half tapered, but i am fat and need that extra belly coverage.
What every you choose cut your 3 layers to size and cut a circle for the footbox with the same circumference as you foot box width from all 3 materials. Then sew the footbox circle into the liner (inside piece of nylon) and sew up 12-20" (footbox length). DO the same for the shell (outside nylon) but when you sewit sew the insulation in at the same time. This will give you 2 pieces that have just been sewn at the foot area. Lay the shell and insulation on the floor/table, insulation down and lay the liner on top (right sides of nylon together). Slide the liner footbox into the shell footbox. all is left is to pin them together, add drawcord tube at head and any tabs for undercords (also will want to add a piece of nylon triangle above the footbox to take the stress of where the 2 sides meet. then sew it all together leaving 12-18" opening someplace like a side that will be easy to close from the outside. turn it right side out and close that hole and goto sleep.