Aldo, hello there.
If you get yourself the Ducati Performance catalogue from a Ducati dealer it has dyno' charts for the various exhaust systems / chips / filter etc.
I have 85db Sil's and 14T on the gearbox on my S4 and it sounds and feels fast enough for me, the 14T has to be the cheapest and easiest performance aid you can do.
another option is to get EURO spec arrow cans. they come with chokers in the exhaust tips that keep the noise level reasonable. why bother? well you can take these chokers out with the removal of one small bolt if you want to set of some car alarms