Possible problem, it was agreed in the old version of that calc that Stain was swinging his sword. As the anime showed, he was running forward with his sword held out. He was not taking a swing, so the speed used was the fastest human running speed at 12.5 m/s. Which lowers the results to Mach 6 or just Hypersonic.
@Metalballrun: This is how I see the scaling, since Shigaraki's strength is heavily implied to be Kamino/Movie All Might level in strength. And that Shigaraki was still stronger than 45%, which means 45% should be weaker than Movie AM.
The USJ Nomu is equal to USJ All Might, and the Doctor can easily say that Nomu has strength on par with All Might. Chapter 21 "After all the trouble we went through to make him as strong as All Might..." The anime allows us to hear the voices and it's the doctor who says this.
Chapter 276: "It's not quite on par with All Might, sadly! Excessive remodeling of his body would've overburdened his brain." So basically the doctor is fine with calling the USJ Nomu as strong as All Might, while he isn't okay with saying Shigaraki is on par with All Might.
I've already said I don't believe the difference is huge, but the scaling is like. USJ Nomu>Movie All Might>=75% Shigaraki=Kamino All Might>45% Izuku. At best Shigaraki scales equal to the movie feat, while 45% Izuku should be scaling below it. While USJ Nomu and AM scale slightly above the movie feat.