One of the airshows I went to (1980s) one of the F-4 Phantom II displays claimed a Phantom could hit Mach 2.5.
Was skeptical, thinking perhaps Mach 2.2.
Was Mach 2.5 achievable?
Many years ago I read thru the NATOPS manual (while a duty driver in the ready room) and saw the speed/altitude charts for the F4B.
Looked like a very tight corner where 2.23-2.3 was possible.
Recall a navy pilot saying if you got it up there with the temp/altitude just right, the windshield over temp light would stop the fun.
I never went Mach 2.5.
Most of our work was done at 400-500 KIAS. External tanks acted like a big speed brake. A clean Phantom at full afterburner would run out of fuel in 12 minutes, or so they say.
The F-4 set a speed record for military aircraft in the 1960’s (1602 MPH). I think the Soviets eventually bested that.
Probably, going downhill.