<You asked for it, its gonna be long>
Well its more of a personal experience. Like I have built settlements with tens of thousands of pieces. You can get some idea from my imgur profile (I have just publicized a gallery of another now abandoned project).
I have this bad (good?) habit of making only those designs which are somewhat technically possible. Thus I add additional supports, beams etc till I feel satisfied. As you can see in the above photos that I am an avid fan of beams...
While reaching limits (depending on your VRAM) there are certain behaviors which start popping and I can understand that the game engine is reaching its limits. Like:
- If you have tcl enabled and you cycle it while in midair, a short animation and sound plays as if you landed on ground. The delay from the point you disabled clipping again to this animation marks the load the engine has. It progressively increases with more pieces.
- When you come near to the limit, the engine then starts reducing the texture resolutions. Most of the textures will then become bland, there will also be stutter. The stutter is more related to how your settlement is planned, a spread out one does not exhibit much of it.
The last spectacle island settlement I built (150+ settlers) served to be the food supplier for ALL my settlements, It had fisheries all around except the north side of the island. Also 2 house rows along the coastline with brick pathways and pier embankments. The central area had a mountain. All terrain was custom. It worked flawlessly with minimal stutter... It perhaps had many times more pieces than any of my previous mega settlements. I used a low resolution texture replacer then.
- Finally when you continue like a stubborn mule, badgering and hammering the poor engine, you finally see artifacts. Its difficult to describe. You are walking in the view of the settlement and suddenly the walls will vanish, and the interior will be visible. If you move your view sideways, it will become mush.
- After one encounters that its best to start downsizing as you never know that the next save load or any random subsequent save load will start crashing in this settlement. Also if you have too many SS plots then it is almost certain that SS will bite you in the *** soon (I guess due to scripts) and most probably the situation will be irrecoverable...
So I am now using a very low resolution texture replacer and thus I have achieved what I could never imagine with that concrete build.
<Side story: Another Day Another Lost Cause>
I remember once I built a mega circular bridge (6x256 width) on spectacle which ran all around the coastline. I remember each angled section had about ~750 pieces. And there were, I guess about 18 such pieces cloned with clipboard.
Then there were 5-floor triangular towers which were about 3-6 floors above ground attached to these bridge sections. Each tower had 3 plots, a base section and a sitting area on the roof. Each had about ~1400 pieces.
I encountered the artifacting when I placed the 5th tower... Thereafter SS soon bit me, and incarcerated my character for eternity... no amount of bribes, brainwashing could save him...