I do wonder if a REAL 8H12 would not be measurably more efficient than a Bensen rotorblade. Bensen blades are dead flat on bottom, and the top skins tend to flatness, too. On top of that, we have skin gaps, lap joints, rivets and no tip fairing.
Chuck, in the 70's you published some drag data for different rotorblades in the SRC newsletter. You showed Bensens coming in dead last in the efficiency department, compared to other metal blades of the time, a set of wood blades, and your own homemade "skinny" blades.
I flew Bensen 22-foot metal blades, pitched up to about 2.25 deg. from the stock 1.5, until acquiring McCutchen blades. My poor old 1835 VW really struggled to climb out at all in hot weather, with 160-lb. me and those Bensen Erector-set blades.
When I bought an Air Command with (of course) 23-foot McCutchens and a mere 40 hp 447 Rotax, the performance difference was impressive. McC's, IIR, have a much more accurate 8-H-12, faired tips and no parasitic stuff all over the skins.
I imagine that the significant trailing-edge reflex that seems necessary on 8-H-12's is a power-suck, too. It creates a download, leading to trim drag.