Two 4'x8' 3/4" ACX plywood sheets later:
The star of the show was definitely the Pony 9.5" pull saw from Woodcraft. This enabled me to make tight, clean cuts, and most importantly, I could cut the large sheets by placing them on the ground on a series of 2'x4's layered two deep, and then climbing on top of them.
Even though I used two folded towels for pads, my knees are quite sore today.