Frame rate in FS9 is somewhat of a different animal than in AH. Remember that in FS9 there are way more scenery items to be drawn than in AH. You can have multiple roads, water, buildings of all sorts, even power poles with street lights! There are even transmission towers for electricity.
If your system will handle it, set your frame rate at about 30fps. IF it stays steady there, be very happy. Many folks leave their frame rate at 20fps to allow more resources to be drawn in the distance.
There is a multitude of tweaks for FS9 and FSX that directly affect your FPS. There is replacement terrains, distance tweaks, all sorts of adjustments that can be made to get better performance. But you had better be willing to spend time reading and making mistakes.
I've spent several years messing with FS9 and now FSX. I've run FS9 on systems that were a bit older all the way up to brand-new-GAWDwhatamachine type of systems. Results vary GREATLY in performance. Ive had older machines that would run FS9 so smooth you'd think you were really flying. Had brand new machines that would burp and squeal as soon as I started the flight. Tweaking the settings is something that most everyone finds themself doing in FS.
The sims are very enjoyable even if not combat oriented. I regularly do flights on VATSIM that last from 1-4 hours. Have made flights lasting in the 8 hour range several times. The entire time talking to live ATC.
You just need to decide how much time you are willing to give to a project. Especially one that the manufacturer has shut down. Microshaft has shut down ACES studio which is the development house for the FS series and the Train simulator series. There is still a very dedicated community making add-on software and aircraft, but a new version of FS doesn't seem to be a reality. If you get happy with the FS series, I would suggest at some point that you download the X-plane demo and give it a whirl. Flight models are MUCh more accurate, and the terrain graphics beat the MS stuff hands down.
