That 1260 Ducati Diavel, that we cannot shake out your mirrors, not only wears the same width rear tire we do but has got 60.5 mm Moto Corse headers even though it sports half our engine size. If we can improve the expediency and efficiency with which we expel spent gas, we open up many improved breathing options. Improved breathing = improved power. Our throttle bodies are also smaller than the previous generation Rockets'.
GT owners are already unhappy with their rain suits' right legs melting away - with the flattened stock headers. Imagine what larger diameter, liberally radiused headers will do to their plight.