On the contrary, all popular physics engines today (including the one in FO4) do not tie simulation framerate to rendering framerate. That would make the simula

On the contrary, all popular physics engines today (including the one in FO4) do not tie simulation framerate to rendering framerate. That would make the simulation incredibly unstable. Instead, the physics happen in their own thread at a fixed timestep. It's up to the game developer to have enough sense to write non-blocking multi threaded code, but if they do things by the book everything just works. This includes FO4, which contrary to your post does not have a 30 FPS cap (except on consoles).