Unfortunately I am another person who has the same problem (which is why I signed up with the forums). I tried the AI thing, it's usually on 100% and I put it back to 0% to check if it was the AI, but unfortunately I also have this 'lag' coming up.
For example, when I am parked in the standard Cessna on the GA ramp, and go to spot view and turn around, from time to time my view stops for half a second, as if it is a lag. There is no FPS drop though, and it is only with this scenery. The other FSDT Hawaii airports don't have this problem, neither does any other free or payware airport.]
If it was just outside view, then it wouldn't be so bad. But I experience it also during approach and such, and it is a bit annoying to have the smooth movement stop every now and then for half a second.
I didn't try the smaller textures yet, I'll give that a try first to see if that makes a difference or not.
Also, I don't know what kind of setup KDFW has, but I too work with a 4 core pc and have no troubles running FSX either but, like him, I also don't feel much for buying all the other addons all over again for FSX as it can get quite expensive. In time perhaps, but for now I will stick with FS9 (like many others do as well for similar reasons).
Anyways, like said, I will give the smaller textures a try and will report back later =)
