I don't mean to over simiplify the OP's question, but I've had just two new CVO's and both with O2 sensors and I would like to share my experience with both.
The first was an '08 SERK and I did the V&H Ovals with a PCIII with their website's canned map. I then did a dyno tune while in Sturgis that year and it did improve my mileage, but both setups would pop and backfire during decel, but still a lot better than the OEM setup. The sound was great, but a bit loud on the V&H Ovals.
The second and current ride is an '09 SERG. This is when Fullsac started to get big into the site and lots of customers with identical bikes were setup by Steve and he offered a great package to just bump things a bit.
I bought Fullsac's 2" baffles with his TTS Masterune and his dyno proven canned map, which he provided at no charge with the purchase of the Stage I kit. I did my own thing with the CAT and welded back in the piece after I removed the CAT. This was all done with the header pipe still installed on the bike.
I have to say that my SERG runs better than I could have imagined, based on my previous setup with a dyno tune. The sound of the 2" baffles is loud on acel, but quiets down very nicely on cruise speed. I get mileage in the mid to high 40's riding two up. There is absolutely NO backfiring or popping on decel.
Another plus is that you get to have the sleeper look as everything visually on the bike looks stock, but runs great and sounds great. The mufflers still have the EPA stamping so a quick visual cannot tell anything has been changed and the header pipe looks stock as well.
It was the BEST upgrade I've done and would do it all over again.
Fullsac has a great product and it took me just a long evening to get it all done. The laptop down/up load of the new map is quite easy and there is no telltail moddule left on the bike to cause problems. My PCIII let me down and I had to remove it to get back home one day. They replaced it, but I still had the issue along the freeway that should not have happened.
So my simple solution was Fullsac. Don't get me wrong, the V&H setup is kicker, sounds great and looks cool. But for the money and effort, I don't need anything else on my bike to make it run "better"...
Good luck with your choice, because as others have said, it is your choice. You are doing the right thing by asking for opinions and experiences on this site. So I've given you my 2¢ and that's about all it's worth.
