I took the can off to spray paint the endcap, and just for fun, I started it up with just the straight pipe coming up under the seat. Honestly, I was surprised at how quiet it was. Of course, it wasn't whisper quiet like stock, but it wasn't all that loud either. It takes just a minute to take off the exhaust can, so try it yourself and see what you think. Then go from there.
Also, I have a hard time believing that it will ultimately hurt the power output. As long as the computer is making things happen right (stock tune or not) then it should be nothing but better for it. The best performance comes from an open pipe. Back pressure is only an issue when you're trying to make a streetable exhaust system act like a super free flowing open header system. Bottom line, open header wins every time, but with the right tuning, a full length exhaust system can come damn close. This is most obvious in cars where the exhaust system runs such a long length, and it's very noticeable and difficult when trying to tune a full exhaust system perfectly.