On a dyno I saw on planetsand, t6's did perform the worst out of all the pipes tested with an agressive play ported 350. Numbers were as follows, the t6's made 68 hp, t5's made 71, fatties made 72, cpi's made 72.5, and shearers made 73. The problem with the t6's is that the don't rev out like the other pipes and they sign off really quick. The fatties signed out 1000rpm later than the t6's and they actually made the most torque out of all the other pipes. T5's revved out a tad longer than the fatties did but they didn't make enough torque to take advatage of the extra 400rpm they pulled over the fatties. Cpi's and the shearers revved out well over 10,000rpm and they put out a smooth torque curve from about 7000rpm up. Cpi's peaked at around 10,500 while the shearers pulled an extra thousand rpm on the cpi's. I'll post a link to the dyno tomorrow. You have to sign up on planetsand to view the dyno though.