DCS[0] in multiplayer. Horribly single-threaded at the moment, no CPU on the planet is good enough for a really busy map, running a bunch of detailed flight and systems models. They’re working on it, but they’ve been working on it for years. Typical small market development constraints.

[0] https://www.digitalcombatsimulator.com/

Yes, definitely. Many FPS gamers as a matter of visual advantage wish to run their FPS game at the highest possible framerate, or at least as fast as their display. This usually means 144-300+ fps. And it needs to be pegged at a consistent rate (so even in the most graphically intense moments). Achieving this even on low settings and with a high end GPU is not always possible, and a high end CPU and high end RAM are required to be consistent, especially for 1440p and 4k.

There are some that won't consistently stay above certain framerates in some circumstances. World of Warcraft for instance performs tangibly better on newer CPUs in settings like 40v40 team fights in battlegrounds for example due to how CPU-bound it is — on a 9600k it'll struggle to stay above 120FPS and occasionally dip below 60FPS.

Cities Skylines once you get to a fairly large city size. Arma 3 can also get extremely cpu heavy depending on the map.

I was using about 60% of my cpu running Cyberpunk 2077 at 1440p 120fps. Maybe if you wanted to run it at 8k using an RTX 4090.