That has been the eternal question since I bought my 18X.
These are big bikes and look the best with a big can - cans, in my opinion of course. I too have a retro that ended up with stock neo's, kinda as a whim. I kinda like the neos the best and have gotten as many compliments the same.
I also think MY X absolutely runs the best and gets the best mileage with stock pipes - no question about it, supported by too many $$ invested.
I haven't done a dyno tune, but figured a nice quiet bike with a decent stereo in a fairing, was more useful.
My opinion and preference of course..
Great bike by the way Joe,