Not too sure I agree with that. I know that you can have two different engines with the same power and one will fly the same plane faster than the other. One instance that springs to mind was when Larry Kramer was flying his Falcon powered(22lb I think) Bobcat at the same time as I was flying my Bobcat with a 19.0lb Supersport. The Supersport powered plane was by far the fastest of the two and anyone who has seen Larry fly will know he's not one to hang around! So I do think that exhaust gas speed can make a big difference.

Jason