That's not practical with the new approach (which uses pip to install pip/setuptools and pip doesn't have a "use the first match" approach). If it's not acceptable to change the behaviour, I don't think this whole approach is viable.

What we could do is add new ```--setuptools-req``` and ```---pip-req``` options that let you specify a requirement. You could then specify an exact version. But it's still different behaviour. And I suspect it's overcomplicating things for a relatively rare use case.

Is the current behaviour by design, or just a consequence of the old "search for a sdist and install it" algorithm? (I ask because I don't particularly agree that the current behaviour is sensible - it's the only place in the packaging system where we use a "first found" algorithm rather than a "best match/latest version" one, so I see it as a wart).