As far as I know, you would need to download AI specific models. Else, choose one without VCs, delete the panels, and any other unnecessary folders.

I'm not sure about actually altering the model itself, someone else will have to field that...

Well. altering the model is (unfortunately) so difficult it is not really worth the trouble.  You would first have to get a program that can decompile the model (don't really know of any) and then edit ALL the parts to lower the poly count, then recompile.  It would be a major undertaking, and would take up a fair amount of time.

But I have noticed that it isn't so much the poly count that takes away from framerates; it seems to me the higher the quality of the textures, the harder it is to load.  If I were going to do this (and I most certainly am NOT ) I would edit the textures to a smaller size and take away the alpha.  That may spare your framerates a little.

But if that doesn't work, your best option is to go find AI-specific stuff.  Older versions of the aircraft, such as ones made for FS2000 or 2k2 might work better as well.  They tend to be a little less comprehensive and more framerate friendly.

Good Luck

Locke