Best performance mod I did was remove the throttle stop that was cast into the throttle body.
I've posted about it before, but fresh off the lot, when I removed the throttle tube, the butterfly would only about about 30%. There was a tab cast into the throttle body that limited how far it would open.
I reached under there and broke that tab off with a pair of needle nose pliers. Totally different bike, it was not terrible before, but not great either. I hit 58 mph (indicated, not sure how accurate) on flat ground the other day.
My machine is a 2020 US model Cforce 400. I don't know if it's only US models, or certain years that have the limiter, but doing away with it was very worthwhile. My dealer would not do it themselves, but said they would still honor the warranty if I did it. Although my warranty just ran out.