Good question Dave. Please forgive me as I've forgotten which yammy you're riding, it's 9 degrees outside so my brain is a little bit cold.
Judging from your avatar it appears your bike has true dual exhaust. When I did my research for aftermarket exhaust after purchasing my 950 tourer, I found that for maximum performance, not mpg, but performance, opening up the exhaust is only part of the game. I spoke to three Yamaha mechanics and researched the Internet in depth. All of the mechanics stated that there wasn't huge differences in exhaust brands, however when you open up the air intake system along with the exhaust, you'll get the best performance gains. I didn't notice if you'd done any mods to your air intake, but I'm just passing along what my research found. Personally I like the looks of true duals, however my bikes research showed keeping the 2into1 with an aftermarket slip on gave better torque, and throttle response. At the time, and even now I couldn't afford the $700 price tag for the true duals and an open air filter kit and a fuel processor since my 950 is fuel injected. At that time to get my ECU reflashed was around $500-$600 with an undetermined down time while it was being sent off for the reflash.
I do know that after I added the cobra slip on, I had a bit more performance and great sound. After the open air filter kit and fuel processor to compensate for the upgrades, much better performance all around. This was just my findings and I hope this helps. Please keep us updated on what you decide on.
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