Re: What creates "Drone"?
 

Dyno-Max, Magna-Flow and Flowmaster are the common go-to mufflers for C-3's, unless you opt for side pipes.
All sound great, and 2.5 is offered by most all manufacturers.
2.75 3.00 would be custom systems, but 2.5 as the last poster stated will be fine for your application.
Marty