I have a pretty fast computer , P-4 - 3.4ghz, 2-Gig Memory.
My FS-9 runs fine at the high quality settings, but FS-X does not run well with one big exception.  The 3-D frame rates for the instrument panels have been substantially improved and now the flight instruments respond quickly and smoothly to control inputs.

Frame rates for outside terrain is much slower and choppy.
The instant replay feature ( which I use a lot to analyze how I have flown) is terrible. Its more like a slide show than a smooth replay.

I have adjusted many of the quality settings with little improvement.

Because of my less than satisfactory results with FS-X, my FS-9 will still be my primary flight-sim. Because of this, I hope that you keep development and improvement of your FS-9 products as your primary focus.