Rule of thumb if it needs to look round make it look round that supports the materials being applied.
If you have an oil drum that looks like you can turn it with a wrench your not there yet.
Second rule use the magic numbers
24 edges can be made 12 edges that can be made 6 edges that can be made 3 edges.
You have your gun barrel or oil drum and three levels of LOD
Third make it more than what you think you need with the ideal that it’s easier to make less out of two much that it is to make more out of not enough. I can LOD a high poly model faster than I can add detail to somehting that looks like it’s been hit with a 20 pound sledgehammer.
The reason, in my opinion as to why there is no true numbers as it use to be about what you could fit on a CD than it was about hitting the number that would decay the performance of the game. Now counts as to performance are not that fragile and I would be more worried about the total number of draw calls as to texture as I would as to the number of polygons that fits the design.
Proof of concept.
