Would be nice to include some numbers if appropriate, maybe as a range?

I'll add some ballpark figures.

I'm slightly wary of being too precise, because you'll only e.g. enjoy the typing import speedup if you've also avoided importing contextlib and re (and anything that might import contextlib and re) elsewhere in your code. If you're writing a small CLI tool where startup times are really important, it's more likely that you're already being careful about that kind of thing, so it's more likely you'll see an improvement. But as soon as you e.g. import asyncio, it's game over.

Yep, a rough ballpark is perfect. As you say, this really helps CLIs rather than big apps or libraries. People who really care can click through to the PRs to see the full details.