Last generation aircrafts : Are they smooth ?

I have just tested three of the latest aircrafts for FSX to compare their FPS performance.

I put the aircrafts in front of the runway 28 of La PAZ, loading Latin VFR scenery.
It's 12 hour, no weather, no traffic manager, i am not on any network.
The all purpose is to check the frame per seconds score from the virtual cockpit. Rules are simple.

Quality wings Americal airlines + winglets gives.........: 20 - 22 FPS
Airbus X Aerosoft US Airways gives........................: 25,5 - 30,6
Ariane Design (American Airlines + winglets) gives....: 24,5 - 26,5
For comparison, old PMDG 747, PW Oasis gives.....: 19,5 - 24,5

That's it !
Obviously, Airbus X and Ariane designs scores are good but Airbus X is (still) not a hard core aircraft and Ariane Design's cockpit's textures are of lesser quality. These scores are pretty good for me, considering that our eyes cannot assimilate much more frames. But the test took placed in front of a runway, in a middle of nowhere. At gate, in the airport, these FPS droped to 8 - 14 (on my computer).
This is not good enough to enjoy the flight. Who's fault ? Scenery designer or aircraft developer ?
Mason

La Paz SLLP, Latin VFR.

Test conditions were exactly the same for all aircrafts and I relaunched FSX each time.
In FSX, I put Fps on illimited, no shadows on aircrafts but full scenery details.

My computer : Quadcore Q8200 2,33Ghz, 8 gigabits ram, Nvidia GTS250, monitor HPw2207h.