The new Duc (1st) I've bought has 50mm Termis on. How much of a difference does a bigger bore make to the sound on this bike? Increasing speed/performance is not important (hence the reason the R1 is staying), I have bought the bike for its looks and 'that' sound.

On the Termi website:
45mm, 50mm, 52mm, 54mm, 57mm, 60mm, 63.5mm!

The louder the better, over here noise is not an issue.