I suppose prrof was needed in the US, where some believe even the laws of Physics are different

Diesel trains have operated at 125mph for several decades in the UK. Those Paxman Valenta powered HSTs have always been a pleasure to ride. They have since had their power packs upgraded to MTU ones.
The Rolling Stock was never the problem. GE Genesis and Dash 8s are rated for 110mph,
City Sprinters the Amfleet/Metroliner coaches 125mph. Even a rolling Apartment building like the Superliner coach is rated to 100mph.
Amtrak Day zero EMD E8A a US made locomotive that traced its line back to 1937 was rated to 117mph.
The problem is the turns, rails, stations and signals.
The Acela, Amtrak’s flagship and the fastest operating train on the North American continent. With a top speed of 150 mph Takes about an hour and a half to traverse the route segment from New Haven CT to Providence RI. The Northeast regional using a City Sprinter locomotive and amfleet coaches take the same Hour and a half.
It’s like trying to drive through midtown Manhattan at rush hour. Doesn’t matter if you’re behind the wheel of a Lamborghini Hurucan, Cadillac Escalade V, or a fully loaded garbage truck. Potential top speed is irrelevant if you don’t have the conditions in place to allow for you to accelerate to it.