Yeah, I think people put overstate drivetrain losses a bunch. Factory power ratings are fudged this way and that so don't mean a whole lot. Even wheel dynos don't tell the whole story - i.e. air resistance while driving down the road. Synthetic fluids reduce drivetrain friction losses as stated above. The main thing, is that smaller, lighter components typically use less power than larger, heavier components. But at the potential cost of reliability due to strength. For example, my El Camino has a turbo 400 transmission and 12 bolt rear end. If I ran a turbo 350 and a 10 bolt, I could put more power to the ground because the smaller, lighter parts sap less power. But the odds of the staying together behind a 502 with nitrous is not as good. As for how much power each component saps, it's going to be different with different units (four or five speed, size ring gear, etc.), fluid type and weight, temperature, etc. Hell, tires have different rolling resistance, as well as different road surfaces! Try not to lose any more sleep over all this!