the F-4 was promulgated as having a higher sustainable Mach speed than any comparable craft with a similar air to air, or air to mud weapon capacity.
That makes it a debate rather than a question answerable by data - I could claim the B-52 as the winner. Also state the height.
In Vietnam the Thud had the reputation as the rocket ship whilst carrying a payload. The F-4 isn’t that fast once you hang a couple of tanks, pylons and weapons on it. In UK AD, in usual configuration, I doubt I ever saw one go much over 600kts.
At low level I’ve controlled F-3s chasing down F-111s and B-1s well in excess of 700kts - to the shock of the bomber crews as they rocketed past...
At altitude I’ve seen a Lightning chase down a Mirage-IV which was doing M2+. But the Lightning could only hack it for a few minutes for the intercept, whilst the Mirage was cruising. And I doubt they had the throttle to the firewall.