>But your software would still run 10% slower than it needs to

There's no absolute objective "needs to" or even any static baseline. Python can have, and often has had, a performance regression that drop your code by 10% at any time. It's no big deal in itself.

Also consider a further speedup of e.g. 50% in upcoming versions (they have promised more).

If you're OK with the X speed of today's Python, you should be ok with X + 40% - even if it's not the X + 50% it could have been due to the 10% GIL's removal toll.

that's not an argument either, as your software is already 10000% slower than it needs to be as you have written it in python.