Allow me to add a little correction.
multi LODing is possible since FSDS1.4 if I recall it right which was available since late 2000, just most modellers didn't see the need to bother with it

The first community multi LOD plane was Joe Amodea's and Jorge Alsina's P-40, some of the oldhands may remember, Defense of Australia if that rings a bell

Whatever, FSDS cheats when it comes to counting triangles, actually it counts just poligons, regardless of how many triangles these persist.
Having said that you can double the results of the FSDS poligon counter and you are close to the true results, mind you, each game render engine deals with triangles, that's what counts and what sucks the fps.
As a side effect many of the older FSDS birds are way beyond budget without the designer really being aware of it.
Other trap is the famous self-cheating (I'm guilty, too, LOL).One tends to leave out this one badly needed LOD level, or makes the other one yet with a way too high polycount, the possibilities are endless.
Why all that talk?
You can have good detail in the main model in CFS2 but make shure to follow the LODing guidelines and your plane will work flawless fps wise, there is really no need to mess with AI planes.
Feasable guidelines would be fairly as follows:
LOD_100 = 7000 - 20000 (whatever you think) triangles
LOD_90 = 3500 triangles
LOD_70 = 1500 - 2000 triangles
LOD_50 = 500 triangles
LOD_25 = 150 - 200 triangles
LOD_5 = 10 - 25 triangles