Annonymous,
I dont know if this will help or not, but I was running a 4400+ with 2 gig XMS DDR and a 7600GS 512 MB card and flying FS2004 at all the highest settings. The game ran lawflessly at all times. I have no idea what FPS I was achieving but I guess when the game ran perfectly, they must have been enough.
With your system (very similar to my old one) you should also be able to run the sim at the HIGHEST settings flawlessly too. And as Doyley said, you dont need an FPS above 24 really, that by the way is the standard FPS for all Movie Theatre settings, anythign more than that will be undectable anyway.
Be careful when using AA and AF - they will both effect and reduce your FPS and in some cases, will reduce them a lot. If the game runs without a hitch I wouldnt be too concerned about FPS rates as you obviously are getting enough.
Cheers