The F-4K and M max IAS was, from memory, 750 kts at sea level but increased up to 810 at 11 000 ft (not sure why). Went along nicely at 750 KIAS at low level even with 2 tanks.
I will need to dig out the books but IIRC the F3 Vne was originally 800 KCAS (no tanks). Would be interested to know the dive angle for some of the higher speeds reached that are quoted above because when we did the clearance to 800 KCAS with 2 Skyflash and 4 AIM9s it was not that easy to get there.