My Iron came with rush slip-ons. 2.25" baffle and it's plenty loud. Mine are the 29 series slash down slip-ons. The guy I bought it from did not do any fuel management due to adding the slips(of course the a/c was still stock). The bike ran well for what it was. BUT, it is now under the wrench getting the 1200cc treatment!
I have the cycle shack slip ons, 2.5 slash cuts. They've been great and aren't too expensive. I was running them with the w118 thunder torques, but just pull out the baffles and put in the bigger w158 thunder torques and it's like a new bike. I also have a heavy breather a/c so I bought a tuner awhile back.