As GBS says it’s ballpark stuff and FWIW it’s what I’ve always used....as for needing a “reference” or “reference material...” well TBH it’s a function of the basic school Physics and basic maths:
https://www.ck12.org/physics/speed-o...f-Sound-MS-PS/
As a clue well, Mach 1 at cruise alt temperatures is
very roughly 10 nautical Miles a minute or 600 nm per hour..the rest follows....