600 CFM vs 750 CFM...

7milesout, IMO, and experience you are correct. I don't know about "cranking up" though. (You mean starting the engine right?) I don't see a difference there myself. Also secondary size. The Venturi part may be different IDK. I'm just to lazy at this point to go measure.
(Concrete work today...)

The point where a 750 is better than a 600 is 100% engine combo dependent.
On a lowly stocker, mild performance engine, it would only be at the top end.
5 - 10 HP.

If the engine was more of a street brute or strip runner, the difference would be immediate as per air needs.

*I think* engine masters something of the sort. In one episode where they swapped stock Edelbrock heads for ported versions, in the Dyno graph when comparing the two, you can see where the ported heads start to really take off. While the carb remained the same, you can see how the ported heads consumed more air and made more power. It is kind of the same thing. More head equals more air flow which equals more power just like a carb would, IF the engine can consume it.

The carb was MORE than enough for the stock head.

My mostly stock 5.9 has a Edelbrock 600. B body, AG intake, Hooker headers @ 1-3/4 - 2-1/2 exhaust pipe, electronic distributor/chrome box. Stock broom stock cam. 3.55's.

My solid cammed 360 uses a 750 and could probably use more. 4 spd, 4.10's, etc...