The highest TAS of a propeller driven aircraft will occur at the highest
altitude at which the power being developed can occur. In other words, if
you want to fly at 65% power, fly at the highest altitude at which 65%
power can be developed.

That makes sense.

I actually found an article I'd forgotten about, about turbonormalization at
the website I'd linked to earlier which shows it with power curves and other
charts.

http://www.nar-associates.com/techni...urbo/turbo.pdf