I have 2.25 pipe true duels with a custom x-pipe and flowmaster 40 series deltaflows. It sounds real good but a bit quiet for me. Thats why i added the cutouts There is very little resonence. I gained a little in the upper rpm range but did lose lowend torque from my previous exhaust setup. I felt a gain after i put the x-pipe on.

If i was to do it again i wouldn't go with true duels unless I was modded more imo.