I have the RCX 4.5 slip ons with tormentor header. Runs great and header definitely improved low end torque. I road the bike for 1000 miles with just the slip ons and lost a little right off the bottom. Mid range was better with the slip ons, but now tuned and header is great. Very strong running motor.

 

I have the NHs on my Deluxe .. I don't / didn't notice any low end loss.