My bike is pretty stock,, engine wise,,, except for the Del's. My FI certainly should adjust the mixture,, and I did not have any performance problems. In fact,,, the bike seemed to pull noticeably stronger through the mid-range. I guess I am a pretty spirited rider,, and would miss that extra torque now. I think after-burn is about the same,, but deeper in tone and a bit less muffled than with the oem cans. I don't have any surging. I am pretty sure,, that if your o2 sensors are disabled,,, there is no way the ecu/fi can compensate for the reduced back pressure that the Del's would create. Hence you may have a leaner mixture, more heat,, and more surging. Or not. Hard to say.
On the topic of earplugs,,, most touring riders who find a good comfortable set, never ride without them again. I have a custom molded set that is left over from my days in industry. They only filter out the wind noise and engine sounds that you don't want. I still hear everything else fine,,, like intercom, gps,, music,, engine/exhaust tones. It is just a lot less fatigue,,, and saves your hearing as well. Cheers, CAt'