Control.
Big airplanes that allowed as mods, not feeling like big airplanes, more as heavy ships.
I flew in FSX about 2 years (theres the rails too, but adjusted good for all planes)
And I can say, one of the most important things in the big airplane - it's a control.
You should feel all that hundreds of tons behind you at an insane speed.
http://www.youtube.com/watch?v=DzZErR2p4Dg - screenshot
http://www.youtube.com/watch?v=tIruU0xuwc8 / http://www.youtube.com/watch?v=GkHZHPTJepA- saab2000/saab340
http://www.youtube.com/watch?v=UxqyNJyTWQQ - just as suggestion for one of planes
https://www.youtube.com/watch?v=hkdrEhMHfsk - control