Of course the performance statistics I usually took with a grain of salt...
I did after they showed every track asset I used, no matter who made it, as having the worst buffer count.
The unfortunate part is this is a combination of experience and process of elimination which leads to choosing assets carefully. Many of us have experienced awful lag with some routes and blamed the program only to find that some assets were pretty bad to start with.
A big part of this issue came about due to lack of error-checking in the past. Assets were created by users and never vetted for errors during the installation and then only at runtime, and that too was a cursory check. As more and more people created content, they copied each other's works, including some early built-in content with errors causing the problem to multiply.
As new versions of Trainz came out, they became stricter with faults. With Trainz being a rare program that can load previous versions of content, the program allows some leeway for older content due to older content not supporting the newer features with the stipulation as long as the old content meets the correct standard at time, then it'll load fine. This doesn't mean that all content is going to work well, and there are many older assets that lack LOD which leads me to one of my many experiences with this.
I've mentioned this before in other threads relating to bad content but it's worth mentioning again here. On my compact Gloucester Terminal Electric route, which is derived from George Fisher's Gloucester Terminal Railroad, I had one particular section where the program would freeze dead in its tracks but continue on okay beyond that section. Once that hiccup occurred, everything was okay afterwards. I got to a point where I would look at the area first before driving to ensure that the bug was out of the way, or look in another direction when I rode past that location.
Not being one to be satisfied, with a half-baked workaround I did some sleuthing meaning the process of elimination. In this very complex area of catenary, various other splines, buildings, a salt marsh, and plants were tons of things to pick, remove, and try. I deleted content and drove only to find something didn't work, and repeated this process for hours then one day I noticed something. In the Annisquam River were some very tiny buoys. In the scope of things, these would never be seen anyway, but they were there in the original. Just for kicks I deleted them and everything worked fine.
I don't remember who made the buoys but they had a huge number of polygons on them with no LOD causing the program to freeze for a minute until the assets were cached into memory. It's possible that the assets are fine and their mesh or textures were corrupted but anyway after removing those, the route runs quite nicely.