I have the full Delkevic system on my '09. It loses torque on the bottom end vs stock header but makes more 6k & up.
It just depends how you ride. My wifey isn't happy with lots of throttle so I like the top end power when solo.
I feel the wife statement on a spiritual level. I was talking with a guy that bought the 2020 Concours, he's having his ECU flashed by Ivan. Apparently he talked to Ivan and said he doesn't recommend them, as they are a cheaper version of the ZX14 headers and have the power drop. Definitely some food for thought. I'll be focused more on the Sargent seat the gentleman got, he let me ride his Connie after my shift and that seat is really comfortable.
Oh, and the M5 from Two Brother's sounds wicked on the bike.