@theluthier tried this in 2.83.4 and results are similar, linked duplicates are slower to render and use more memory (2.91 appears to be a bit faster…)
Now, it is possible that because I’m on an older P.C., I am not able to use some optimization features that modern hardware uses, but I’d still expect linked duplicates to always be better than Arrays/Mirrors/ normal duplicates…
Guess I’ll have to learn C/C++ and dive into the Blender Source Code and see what is going on..