Most 4-2-1 full systems for Gen2 (that are full length and full can) are similiar in decibel ratings. Like the full R77 mentioned, it's really quiet, and not much louder with the baffle removed. The full stock system on Gen2 is around 48 lbs, average aftermarket full system is around 15 lbs. I think the gen2 mufflers are 15 to 17 lbs a piece. Each aftermarket slip on is gonna be around 1/3 of that weight.
Most manufacturers will post a decibel rating of their exhausts on there homepage, and Yoshimura's also shows the stock rating. You would be better off to look at many exhausts and decibel ratings and then pick the one you liked the looks of. Of course many sound similiar, and some sound noticeably different. The only way is to hear it in person, sound clips give you an idea, but will never be the same. Go to a dragstrip, walk around, ask folks to rev their's up for you.
Brock's Alienhead is one of the louder more powerful systems out there, but is suprisingly quiet and mellow at low and cruising rpm's, but get on it and it gets loud.
Also a full system is a good choice because it will get rid of the catalytic convertor, which is cookin your feet more than you realize.
After you have narrowed it down to a few systems, look here and on ebay, you can get something that's like new for around half price. You also will not need a power commander or a dyno tune, the bike will run fine and safely without them. However, if you can afford it, a good tune will always smooth out the power and gain a few hp.