> How often does it make sense to run each thread ~100x slower so that we can leverage some aggregate state?

What I mean is that even if cross core latency stayed constant, but IPC increased, the opportunity cost of waiting on something to cross cores has gone up too.

I could see if the latency went up over time too though. It's wild to me to have seen some early cross CPU busses on motherboards then become integrated in chips, and brought back out between chips of multiple cores. There's no way to do (N-1)! links anymore. N went up too fast.