Cognitive dissonance <-- you lost me there
I say go with a slip on... you'll still have your cats. Get your jetting done so that the bike runs proper and think about this... an engine that runs too lean pollutes too (high nox). You might make less pollution after the changes even if you consume a little bit more fuel. My bike was pretty lean from the factory
Now go getcha that slip on!
__________________________________________________
Always get a second opinion because most of these people are makin' this stuff up