440 exhaust system

Just want some opinions .

Situation Mild 440 with 480 lift cam kb flat tops and cast heads 2.14 1.81 valves running out TRI Ys Into 2 1/4 pipes.The tranny is a street fighter and the car has 3:55 gears.

How much gain if any would 2 1/2 or 3 inch pipes give me. The 2 1/4 exhaust on the car is good we are just wondering if it would be worth it in performance as compared to cost.

Any suggestions