Ok guys, i've solved my problem. I followed the Nvidia thread tips and it works! FSX runs pretty smooth for me now because I turned the autogen to low. And what's the point of autogen anyway? If you're flying high, you can't even see it. But thanks for your help guys! Oh and Nick, yes I do have the X64 version.
The AG values I gave you may still be too high. I would think you should be able to run Dense but that 3800 is really going to limit that ability and be driven by the AG values used in the config file.
In the FSX.cfg file:
Try dropping trees from 1400 to 1100
And buildings from 700 to 550
and see if you can raise the AG slider to dense
It takes time to tweak the numbers. The main thing is to keep the ratio of trees to buildings at 2:1
Replacing the default landclass file with payware Cloud9 Landclass for FSX will also make a big difference because it changes the way the sim displays autogen. Since it lays it out in a much better defined pattern, instead of making the entire world a housing development, it will provide even more relief to the 3800+
Good to see you are on x64. I am as well for both XP and Vista.