One would RARELY "lose" torque when going from an OEM "Gubment choked" header to a decent quality a/market header. All the companies that manufacture these performance parts would go out of biz if they didn't offer some sort of decent gain.
I don't know about the Rineharts (I hear they're pretty good), but when I changed out my whole OEM Intake & Exhaust set-up to what I have now (see my sig. below), it made a WORLD of difference. Did tons of research before I even ordered my SGS. When we first stuck my SGS on the dyno after putting 2500 miles on the stock bike, my stock rear wheel TQ was not quite 89, even though H-D will tell you a Rushmore 103" motor puts out a tad over 104 ft.lbs.(The Moco dyno'd the motor in a dyno room on a stand with just about "0" REAL WORLD TYPE load).
I listened carefully but understood very little when my dyno guy started discussing terms like "Optimum Backpressure" "ACFM" "CFM" & "ICFM". When we got to the end of my little class, he recommended some STAGE 1 stuff to me...
I took her home and finally ordered & installed the Stage One parts that my dynamometer guy had suggested to me... Trailered her back 2 weeks later & had her dyno-tuned on his $60,000 multi fanned Dyno-Jet motorcycle chassis dynamometer. I watched him go through the complete process. He stopped after each run and explained what he was doing and why. Answered any questions I had. After the final run, and all the VE tables were done, he encouraged me to take it for a good long test ride and bring it back and let him know how it felt. I did, and was absolutely amazed. I then paid the very reasonable bill and he explained my charts and tables. He also discussed further upgrades if I was so inclined.
Cams & headwork "may" come later, but for now I'm quite pleased with my SGS.
Then I rode a totally different animal home while my wife followed me home towing our enclosed trailer. Entirely smoother & much more powerful than the Harley "tractor" I originally purchased. Pulled stronger in every gear at the RPM's I ride at. From right off idle to almost 5K. It even gets better fuel mileage than it did when it was stock. My wife said she could tell I was having fun on the ride home.
Do it right, and it'll put a smile on your face.