[jmatta]

I have Fabspeed secondary cat bypass pipes and a "Pedro Style" sport muffler (also running the Evo Hi-Flow intake). Though I can't vouch for any increase or decrease in low/mid torque, the engine revs much much freely, without the cats. Before installing, the engine (e-gas) would always hesitate on downshift throttle blips; once the bypass pipes were removed, throttle blips are near instantaneous, which would likely be due to loss of restriction.

Oh, they sound great, as well!