Only proof I'll give you is they (tti/dougs) perform better than the 1 5/8 hooker and all the comparable copies in every test situation I've done. They also perform on par with the 5204 Super comp headers. tti's tend to be slightly better because of the steps, but, the price difference to dougs is almost the cost of a decent nitrous unit or a really good converter upgrade. Guys buy tti, I'll spank them with dougs and a better converter or n2o for roughly the same money.
More important... Dougs and tti FIT better than any other full length header. PERIOD END OF STORY!!! No low hanging, under the centerlink tubes. I've crushed my fair share of hooker/copy junk, both comp and super comps. Whether it was dips in the rode or coming down from wheels up launches. Not gonna happen any more.
500 for a pair of coated 5901 hookers that have been the same garbage design for over 40 years is a joke when you can buy dougs delivered to your door for less. Just pointing that out.