Wow 8L/100km it actually is, I think I did it wrong. I didn't really think about what it meant. Oops.
I've done 200km on half a tank, my tank is what 50L? I divided 400km by 50L, I wasn't sure if that's how to do it though.
I have no idea if my speedo or odo is correct, and I don't fully understand what you mean by the "auto diff vs 4 speed manual transmission combo"