I'll answer this for a general audience:
Don't misunderstand the Aircraft Flight Parameters values. These are not performance data for the aircraft, rather, these values affect the way the flight is planned. Don't go through all your planes and set them up to manufacturers specs, instead concentrate on the aircraft you are using. For example setting the Cruise Max Altitude, this is not the maximum altitude capability of the aircraft, instead it is the max altitude you want the plan to allow as an increase in cruise altitude if an obstacle requires you to gain altitude along the route. The Percentage Altitude is the altitude you want the flight plan cruise altitude to be set near to, as cruise altitudes allowed depend on the direction of travel and which areas of the world you are flying and are adhered to along with airways routes - you don't dictate your exact cruise altitude for the plan the airways rules do.
Now, let's say you find you can set 1800fpm climb for a flight but then maybe next time try for 2400fpm climb rate, and then during the flight find that the climb rate cannot be adhered to depending on the atmospheric conditions for example,
- and so you find the performance of the plane
An update to Include multiple setups in the aircraft flight params page will appear in a future update, for example so you can save values for "high" and "low altitude flying", and perhaps "fast" or "fuel efficient flying".
Check out the fuel planning in various threads on the site - the fuel prediction is extremely accurate once you know how to set the range - range is not easily determined without actually flying the plane. The debrief includes a max range calculation for the flight you did - taxi, takeoff, climb, cruise, descent, approach, and landing, again use these combination of values (cruise speed, alt, climb rates) to get a feel for the aircraft performance. During the flight you can get a reading and instant max range calculation from the FSX IF: Main Menu "Fuel Report".
There's a lot more to IF, merely setting a list of manufacturers specs would be boring, and anyway it won't work - use IF to determine the exact performance of the simulated model in the sim.