Reporting charging speeds in mi/hr is not useful because the same electrical power will result in different values for different models of car. Because the mi/hr number depends on the car's efficiency, a Model 3 would report a different value than a Model S/X/Y. And people who drive different cars won't know how to convert between that value in your car model to the expected value in their car model. You should only use kW to describe charging power as that's the same for everyone and anyone who wants to think about charging power in terms of mi/hr can do the conversion for themselves.
Caveat: If you're just wanting to crow that the mi/hr value hit some meaningful number, like "It was over 1,000mi/hr!!!!!!" that's ok. But for discussion where you're trying to convey actual information mi/hr i's not a good unit choice.
