How much power is lost through a 518

Over the years I've read a lot of posts stating that a larger transmission robs huge amounts of power. I actually read that a C6 takes 60 horsepower away. Here's the flaw in the thinking and observation. A 727 is going to most likely come out of a larger car or a truck. They utilize a lower stall converter. If you put that into a lighter car, it will be slower on takeoff; just like a th400 has a larger converter than a th350, a C6 has a larger converter than a C4. With the same stall, the big trans won't produce a noticeable difference in the seat of the pants; only in a fraction of a second on a time slip.