a true resinator does not restrict performance at all.

determining which size resinator you need is a guess even for professionals. There are to many variables to consider. Exhaust pipe length prior to the resinator, exhaust pulse velocity and volume, what components are behind the resinator, and of course the RPM range you want it to function at.
typically speaking a 15" resinator (2-2.25" inner pipe and a 3-3.5" outer shell) will help with the highway droan we all know and loathe.
As far as changing the exhaust pitch, a resinator may change it a little bit, but not near as much as a different muffler.

IMO with the N1 setup, the silencer is your best bet for a nice sound and to keep the cops off your tail.