It would be helpful to have some performance guidelines from IPACS regarding TSC based objects otherwise we may start to slide down the FSX path of add-ons where the smooth frame rates are impacted and new users get cold feet.
Maybe someone has the time to run their own performance test - take a level 9 tile and fill it with 100 poles, then 1,000 poles, then 10,000 poles using a single TSC file. Does FS2 crash? If not, what's the frame rate?
Performance may be tied to the polygon count of those 3D objects - 1,000 simple poles may be the same as 100 water towers. It's probably a function of your graphics card memory size too.
You can have big numbers of trees and cultivated houses because only the ones within about a 6 km radius are processed and displayed - you can test this out by modifying one of your scenProc buildings so it's 100 stories tall.
TSC objects, however, can be seen from +60 km if the object is big enough - if TSC objects eat away your graphics card memory, stutters can't be far away. If we had some guidelines, we could optimize the 3D models (polygon count) and better manage the object count in the TSC files.