How fast was All Might?
That's actually the only information we have on All-Might's speed. 

That scene you're referring to occurred in Chapter 90, which tells us that All-Might ran 5 kilometers in just 30 seconds, giving him a speed of about 600km/hr. 

If I recall correctly, this is currently the best estimate we have of All-Might's speed at his prime, because we know he's faster than that. Only thing to do is wait for new chapters that give additional information.