Ubrales, the minimum system requirement for FSX is bullshit (Sorry, I don't mean you, I mean MS for putting that on and con people with slower hardware to buy it). If you have a machine like what they recommend for mnimum system requirement, you get like 1fps.
The physics eats up your cpu in the game. You need fast multicore processor and a mid range gpu for it to not stutter if you have the physics realism setting on max on high graphics. No point playing it with arcade physics with simple scenery.
I have i7-920 overclocked to 3.82 GHz, 12 GBs of 1600 RAM and a GTX-275, GTS-250 Graphics cards. The GTS-250 is set for PhysX. That's why I said what Microsoft states on the package. From what you mention, it looks like Microsoft is using shady claims in their advertising.