I was wondering what kind of performance gains people are getting out of aftermarket exhaust systems. I fabricated my own and got an extra 2 mph.

If you have done nothing else, then thats about it. Save your money on the so called "high performance" exhaust. All they are is free flowing. Unless yo have a dyno, you won't be able to tell the difference between your freebie and a $500-$600 SS exhaust that WILL crack.

I agree, couldn't tell the difference between a stock gutted muffler, Y Crossover pipe, and the ones I fabricated myself, other than looks. Only ones I've seen that havn't cracked are the ones I've made like these.

I saw a 1.5 mph difference in my gatortail with a voodoo, but a performance exhaust does more paired with other mods like heads and a cam

I have watched my stock muffler fall off my stock motor running wfo. it picked up 250 rpms with no exhaust.
I prefer a quiet muffler to those obnoxious loud ones, but that's me.