I had a pair of XXX muffs w/ 2 1/2" tps... AT 80mph, folks thot they'd been passed by a P-51! Cool sound, but way to much drone. Changed to Dynomax. GTG.
As for power, my dyno tests showed only +3 RWHP diff with the dump open..
I just took off a pitbull muffler...the drone was driving me nuts. I had the shop cut it off and put a magnaflow straight-thru muffler on and it's great...a little rumble but zero drone..and now I can hear my turbo spool up.
I don't notice any difference in performance...I also have a cutout if more flow is needed.