my FXR still runs fine with the original butterfly-Keihin, just a K&N filter upgrade, some cleaning and new seals etc. Well, the bike is stock, only SE 2 slip-ons, but gives a great driveability, pulls strong from low 2000 rpm. Got no plans changing it yet, should be as good in power as CV, just not as sophisticated ( better gas mileage and fine idling etc., things generally not related to HD's )

My springer though has a lot more upgrades ( cam, 10,5:1 comp, SE ignition, thunderheader, porting job ) with the Mikuni HSR42, and the throttle response is extremely crisp, instant. So I'd say only go to HSR if you upgrade more than just a cam, CV's should be good till 100 hp limit.