Have just has installed my new ATI Radeon HD4850 1GB GDDR3 card, replacing my old GeForce 6200. The difference is quality of image and game play with FSX is amazing!
With the old 6200 I could get reasonable frame rates of 20 (sometimes dropping to 10-15 over crowded area's) with traffic off, weather medium and graphics and scenery high. With the Radeon using the same settings I jumped to a steady 38 FPS. Even with graphics and scenery maxed out, weather high and traffic medium I'm still getting a nice steady 20.
And that's with all card settings on default.
All I have to do now is try to understand all the various combo's that this card offers and work out what is best. That's probably the one drawback of such sophisticated technology ............ I'm just not cluey enough to really take advantage of it's real potential.