i didn't read this whole thing, but here's my take....background; i'm 6'1" and i've got short femurs...kinda long torso and normal arms.
i rode 20,000+ miles on 56.5cm top tube bikes with a 100mm stem, maybe an inch or so of drop and setback seatposts. i got a specialized BG fit done few years ago and i was moved to a zero setback post and a 120mm stem with 10cm of drop. the difference was night and day. rode with my usual group the day after my dot and several people commented on my riding. not only was i more efficient, but i felt altogether stronger. it didn't feel like i was pedaling through mud anymore. i was way too far behind the spindles before and although i was maintaining the same reach, i was just moved 20mm farther forward. it moved my weight forward and made me pedal straight down, instead of pushing "forward" on the pedals as well as down.
i've ridden about 17,000 miles in this setup...rides from around the corner and up to 110 miles and i've not had any major issues. sometimes i'm more
comfortable than others, but usually i'm good to go.
i have recently moved up to 58cm top tubes and 110mm stems, but keep the zero setback seatposts.
i don't understand why anyone would want to, or it's comfortable to pedal behind the pedals instead of straight down.