I too drilled mine out. Mine are at 3/8. It sounds great at all RPMs, especially in the lower range while rolling onto the throttle. As fear as performance I have note experienced anything I can tell either way. I don't keep track of my mileage either, so no idea on that.
Jess & Christine(the Chauffeurs)with Tobi & Skye the Border Collies.
2013 K1600-GTL, Damask Red (Guy's ride),
2016 S1000XR, Racing Red (Grrrl's ride)
Plus a home-built trailer, and a few farkels.
Motorcycle Safety Foundation Coach#166465