Only thing I'm thinking of is that most users reading What's New still don't have the context that runtime_checkable isinstance is like 400x slower than regular isinstance or whatever.

Well, only ~15x slower in 3.12 for simple protocols ;)

Feels hard to communicate "this thing is 20x faster than it was, but is still 20x slower than you might think it is"

Yeah... I know what you mean. I feel pretty torn. On the one hand, I agree that this is important context. On the other hand, I feel like this is pretty clearly documented in typing.rst now; that the performance improvement is worth celebrating on its own; and that "What's new" should be primarily focussed on the difference between the Python versions.

I think I'll leave this as it is for now, but happy to accept improvements in followup PRs if we can think of a better way of phrasing it :-)