Yes most of the time I was in the 20s in New York but at least its playable, or controllable, even with all sliders maxed out (FSX is using 1.2GB memory there). I did see a nice gain when I disabled traffic AI.
I do think that DX10 might help rendering the auto-gen stuff and free up some CPU resources, which overall should help to increase the framerate.
Another interesting thing were the CPU graphs in the taskmanager. CPU1 was between 90% and 100% (graph looked like a saw) and CPU2 was around 5% and 10% (again, graph looked like a saw). I set the max framerate to 30fps. How much did you set it to?
While I´m still not fully happy with the framerate of FSX, its looks so much better and is more fun to play it on my new one.