They do make more low-end torque, I've noticed, but they took away from the dual Flowmaster Super-40's sound slightly (at Idle and low rpm) The disclaimer on the kit from Summit racing stated this. Once you step on the gas though, the trade-off is well worth it in my opinion. The Summit pipe kit was aluminized, less expensive than other comparable kits, and of good quality.

I think I could have gotten more low-end power, and less loss of sound with an X-pipe, but with a 4x4 that's very difficult to accomplish without being an artist at pipe bending and welding.

I've never had it on a true dyno before but i have the sim's desktop dyno by it's calculations its 465 HP and 480 TQ. dynoed with big tube headers and a 750 carb its 496 HP and 536 TQ.

you said people has told you that a 750 double pumper was over kill how do you tune your carb?  how much vaccum is your motor pulling if it is over 14in"  of vaccum its not to big needs to be realy as close to 15in" or more to run a 750 17in-18in" is ideal for a 750 any thing more you need a bigger carb any thing lower than 14in" you need a smaller my nova is pulling 24in" with a 650 demon its needing a 750 or a 780 carb but with that much vaccum its getting a good seal. and if you don't mind me asking were do you live in FL.