The stock pipes obviously were too quiet, and were brutal ankle burners for the passenger. I actually had a Thunderheader first, which sounded great, but looked stupid. I went to the Big Radius 2 into 2, for the looks only. I knew well in advance that they do not help performance at all, and in fact, probably hurt it. They look great, and sound pretty good - louder than stock for sure, but never annoying. They do pop a bit with the stock baffles, which is a little hard to minimize.
That said, I installed the Big Breather, Big Radius, and a PC III, and got a JG custom tune and ended up just over stock - barely. My duno sheet is pinned in the SED section. While it was 105 that day, and I never got a stock reading prior to the mods, if you look at the base line with the mods, it's clear the weak link was the BR as the Big Breather certainly couldn't hurt things. John warned me that he saw the same thing with all of the BR 2 into 2's, so I knew it was coming.
Anyway, I merely wanted to try the monster baffles as another fellow with the same exact set up posted a dyno sheet showing a sizable increase over what I got. The only difference was the baffles, so I figured I'd give it a whirl. As I reported earlier, the Monsters are loud, and pretty much sound like totally open pipes. I'm going to manually bump my tune a bit just to make sure I'm not running too lean, and run it for a few hundred miles and see if I can tolerate it. More importantly, see how well the neighbors deal with it. If I decide to keep them, I'll get a custom tune done again with JG at Sturgis in August. If I can't deal with them, I'll just go back to the stock V&H baffles as I have zero confidence the QQ's will offer much for the ~$400 investment.
I hope this helps.