Regarding the mechanical friction losses. Yes there must be some. I mated a sturmey archer aw to a mavic ma2 on the back of my old early 80s kuwahara. I could not believe the feeling of increased smoothness and efficiency compared to the shimano 600 derailers that I removed. The hub weighs about two pounds but is a wash with the removal of all the other crap. I ride mostly in the middle gear which is the 1:1 giving me 42/18 gearing using a 1/8th chain from the raleigh.
I love scrounging and playing with things mechanical.