[Warning: newbie question!] ;-)
In the specs & reference materials that come with an aircraft (which I supposed is are light versions of the official pilot's operating handbooks), many of the V-speeds, range approximations, and fuel consumption info will often be listed in association with a "Power Percentage." i.e.: The design cruise speed for my Piper PA28 is 125 knots @ 75%, 116 @ 65%, and 102 @ 55%.
Does that % correspond to the % of throttle in FSX? (If you hover the mouse over the throttle in the cockpit, it will display how high it is.) I assumed it was the same thing, but then I noticed that most of my aircraft perform a lot slower when the throttle is set to those #'s, even at just above sea level with a very light payload. Perhaps I'm just confused though.