GF,
The F-105 speedbrakes were two of the AB nozzle petals and you had to be out of AB to use 'em. So if you did run down an F-4D at 720k, when you put out the 'boards' you could be sure you weren't going to stay with him very much longer. OTOH....
....In the waning days of the F-105, just for old times grins, we TIK guys in our F-4Ds did a couple of weekend days of rat-racing with the FWH F-105s at low altitude on the Hill ranges. I could pass an F-105 head on, make the turn and run him down in the Phantom. However to be fair, we were clean and they had a CL fuel tank and were the hump-back LORAN birds.
F-4 max Q was 750, F-105 was 800, and I think F-111 was even higher. Have seen 750 in an F-4, never saw 800 in an F-105, best I recall was around 650. However, they were old and tired then. If you count the MiG-23 as a USAF aircraft
, evidently they were pretty quick.