just go straight pipe if you wanna be loud, look on ebay and get some chrome fish or rockets, the cheaper the better and the louder. After a few rides you may think about baffles, I did.
I've got some V&H Ovals on my '07 Ultra that are too loud. I am considering going to the Monster Ovals. Don't know if they will fit an '03 Road King, but I am probably going to try to sell them once I get the new ones.
Its your bike, so put on what you want. Just don't expect many of us to support you when they push noise ordinences in your area, when you put the obnoxious ones on
I have slip ons with baffles and have to wear ear plugs or my ears will ring worse than they already do. Couldn't imagine it would be very pleasant with straights. For me anyways.