[Bruce Edwards]

One problem. The boosters have NO effect at idle. The idle system is controlled by bleed holes in the carb has is not tied to the boosters. When you "tip" the throttle blades past a certain point the main system / boosters kick in to play.
If a carb flows 850 on a bench it should not matter who makes it. 850 is 850 on a flow bench.
I can not see how a 850 is to large for a 460. We use them. Hell we install 750's on 351's and have no flow problems.
A carb that flows more fuel with the same cfm is just plain set to rich. Don't forget that all of the fuel after idle goes in by way of the jets and the boosters size has more to do with the way that fuel is mixed in the venture. Booster size will play a part in mix at different flow rates but it still can not dump any more fuel than is let into the system by the jets.
Of course if the power valve is blown it dumps fuel in the engine and no amount of adjustment will solve the problem.