Strange, what settings have you cranked up. I have just built a 5750 system with Athlon x4 at 3ghz and it runs 25-30fps with settings turned up pretty much all the way on 1680x1050!
Are you using legit FSX with SP2 or Acceleration addon installed, Cracked fsx non SP2 has 30-50% performance hit!
Under settings- custom- make sure scenery- (terrain and water), mesh complexity, terrain resolution and texture resolution are set to default don't turn these three all the way up. Also knock back Autogen density one notch from full under scenery.
Under Graphics tab (Still in custom) make sure you have set slider to unlimited Framerate.
As I say, have FSX running on customer machine with 5750 and Athlon x4 very very smooth!
I run it on x6 with 5850 1920x1080 with literally every single option turned up to the max with vfr addons and get well over 40fps!
FSX is not a brilliantly coded game, like windows, it has not been a ground up design as backwards compatability has always been in th4e forfront due to the huge aftermarket of addons!!!
A tradeoff hit is, and one where by the look of microsoft do not want to go through the process of complete re-design and have even let the FSX developement team go!
Bring on the Free Market competition, now we wait for a true competing killer Flight Sim Product!
Well the 5770 comes default at 850mhz and i just needed a graphics driver update, been downloading new catalyst control center updates on accident, and i get around 30-50fps average with everything cranked up on 1440 x 900. Also best part is i don't have the SP2 downloaded either. Eager to see the difference but i also have problems after i install the acceleration pack, i get fatal errors and it closes...