Given that the native ai is a flyable model that has more detailed textures, requiring more processing power. I was wondering if I could substitute the models for, say the FAIB aircraft, or another model. Place it in a separate folder from the flyable aircraft, making a change to the cfg file, then modify the stock ai traffic BGL to utilise this model instead. And ..how about WOAI aircraft, I'm reading they are old FS9 aircraft that have high draw call issues that impact performance. Is this so?

To answer some of your questions; Yes, you can substitute AI models for the default aircraft used in the FSX/FSX:SE flight plans.

I'm not sure about the WOAI aircraft, but I would guess the impact would still be less then the default aircraft.  If in doubt take a look at the FLAi aircraft for online flying. Update liveries, more aircraft selection, etc.

As for the GA aircraft you'll have few choices other than FS9 models because not much has been updated beyond what Todd Bolgrin has done.  His stuff is available in the AVSIM library.

You can use AI Flight Planner to open the default BGL and substitute the AI aircraft for the default aircraft. 

In truth I'm not how much VAS or performance gain you'll realize.  Even with AI aircraft you'll likely suffer if you set the sliders too high.

In any event you won't need to play with aircraft cfg files.  I would recommend, as you mentioned putting the AI aircraft in their own folders, not that it's necessary, but makes for a cleaner process and segregates your flying and non-flying models.

Ernie

I'm having somewhat of the same problem.  Recently bought a system that can easily handle FSX so I'm finally migrating from FS9.  The AI traffic available for FSX is significantly less than what is available for FS9 so I bought the latest Ultimate Traffic package, but it's missing some airlines I want to see.  My problem occurs when I can't find an airline that has an FSX package and I attempt to move that airline's AI package from my FS9 to FSX and the planes show up with just a white texture (no skin). 

Is there a trick to make the plane's textures show up in FSX?

Any help will be greatly appreciated!!  I'm sure that in the past 10 years many have encountered this problem.