It goes a bit faster than that. I had a teacher, who is a retired air traffic controller, that clocked the thing doing 3500 knots. That’s about Mach 5.2.
3500kts is ~4028mph. Is Mach a set number or does it vary with altitude, temp, and other variables?
I would imagine they save full military power for outrunning SAMs and MiG-31s.
Not surprising, because in a couple of the pilot accounts he said he had the throttle pushed forward the entire time he entered enemy airspace. He said he saw mach numbers he never thought were possible.
The J58’s could give more power than the air frame could handle