I am another one of those people who "upgraded" to FS9.
I was not able to run FSX at all for a long time, and when I finally got a new laptop it ran fine, the same as FS9 did on the old laptop.
The problem is, I love HD airports and AI traffic. In FSX if I tried to fly into any medium or larger airport with add-on scenery and AI traffic then there was really no point in flying.
With FS9 I can turn all the graphics settings up, install every WOAI package, and fly into areas like NYC with Aerosoft Manhattan and the AI traffic realistically busy at JFK and LGA and have no problems at all with frames.
With some environmental textures (HD Clouds!!!
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) FS9 can clean up pretty well. The only places where I REALLY miss FSX is water, gliders, and aircraft carriers. Everything else is great.