Problem is they way carbs are rated, if your engine displaces 500 cfm or air at peak power that will how much your carb will flow no matter if it's labeled a 650 750 850 or even a 250 they will all flow the same just there will be different amounts of restriction aka hp loss.
The only problem is when they are not compared at the same depression with the same method & conditions. If You can get 850 thru' a 250 I wanna see it.....and hear it...