How Many Horses does your Posi eat?

The Ford 9" uses more power because the center line of the pinion is further away from the centerline of the ring gear, that requires steeper angles on the gears and more friction.

The Ford 9" is stronger than an 8.75" because there are three bearings supporting the pinion. One on each side of the pinion gear itself and the third out at the yoke end.

I have seen several articles comapring the rear wheel HP of the same car with a Ford 9", GM 12 bolt and Dana 60 (never seen the 8.75 in one of those comparisons) and there is not a lot of difference, single digit differences.