I have a 2018 FLHTKSE that I rode stock for a about a thousand miles while waiting on parts. I had the stage 3 kit, High Flow exhaust, and Heavy Breather A/C installed along with the Street Tuner and Smart Tune Auto module. No dyno runs to compare, but it feels like a different bike. I had a 2016 SERG with a 117 stage 3 kit and Pro Super Tuner with Fullsac headers and baffles and the 2018 feels very close on the road, except for the sound of course. Very happy with the upgrade. It was more labor intensive than the stage 3 on the 16, but since you already have it apart that isn't an issue. The stage 4 is a great value for what you get but it shifts the torque curve to the higher rpm bands that I don't use.