The numbers in my post have some significant errors — I mashed it in just before my plane was taking off — but the argument is one I have seen carried out more

The numbers in my post have some significant errors — I mashed it in just before my plane was taking off — but the argument is one I have seen carried out more carefully elsewhere. 175 km in 20 minutes would be roughly the top speed of the fastest train ever built. I'm doubting that.