This may be hard to believe, but I actually get better frame rates with the FDG2 B-17 than Bismarck's A.I. B-17.
For some reason, my emachine's graphics card is very sensitive in a way I don't understand. I get great frame rates with the stock planes and certain select addons. It runs CFS3 at 40 fps.
But lots of the addon planes bring it down close to slideshow levels when viewed from long range - when they're just dots in the distance. Strange.
I've had to test everything I have to see if they work with my rig. Surprisingly, among the survivors were the highly detailed FDG2 Fortress and the Malinowski Liberator. I test them by creating a formation of them in MB and viewing them from long range.
I had to give up on Thicko's Jill and Judy, which are multi-lod. But again, the FDG2 Jill partially came to the rescue. It works.
I had to throw out both of my Helldiver models, which has harmed my cause somewhat. I don't have a usable long range Navy dive bomber.
Anyhow, bottom line, it's not always strictly about polygon count, or even multi-lod, at least where my rig is concerned. I have no idea what it (is) about. All I know is, the FDG2 and Malinowski heavies work for me. But only if I set my max frame rate slider at max - 45 fps. Strangely, that makes a significant difference with some planes, but not with others.
It's all very strange.