Hello there!
I'm forwarding the thread #688403 as I've been asking myself the same question as charliecm.
There used to be indications on which size should be used for each weight in the Human Interface Guidelines. We know for instance that SF Pro Text should be used below 20 pt. What about New York Extra Large, Large, Medium and Small?
I'd be forever grateful if you'd agree to give me any information on this subject.
See you around!
S. Lannoo