Captain Sim gives you better looking graphics than most devs, and that's a fact.  It is also a fact that their products will eat frame rates more hungrily.  If you have not learned to get the most out of your system, now is probably a good time to start learning.  A good starting place is http://205.252.250.26/cgi-bin/yabb2/YaBB.pl?num=1208959973.

I have learned to "build my setup around the airplane" instead of finding the "magic settings."  When I'm flying the 767, she's the star of the show!  So some other things get pushed out of the spotlight, like higher scenery, traffic, etc.

I have a decent, but by no means state-of-the-art system, a Dell XPS 430 Dual Core Quad 2.5 w/6 MB RAM and a Nvidia GeForce 9800GT.  I can get very smooth performance with the 767, and my sliders are far from all the way down, I assure you.  So unless you have a system that is really more suited for FS9 than FSX, you might have to spend some time learning and tweaking.  I'll be glad to offer any help I can, and I hope you can get things working well for yourself.