Exactly, no computer runs fsx maxed out with no lag. I used to get 5fps(!) in the 737NGX until i did this:
Turn off lens flare, direct x10, light bloom and advanced animations (Unless you want a moving jetway. (Im ryanair most of the time so jetways dont bother me, ryanair dont use them unless your in Spain)
Turn target frame rate to unlimited so it doesn't have to worry about meeting the target.
Just experiment and put the settings higher and higher, but you have to be willing to lose the odd frame.
Now i get 16fps with aerosoft Madeira X in a pdmg737.
I will try that, ill get a good laugh out of it. EGLL-KJFK in a fully loaded 737.