If the only mods to the bike are a jet kit and exhaust, the only advantages a Stage 2 or 3 will get you is a little less weight from loosing the airbox and an easier time with maintenance. Sadly, no power gains with the the higher stages on a stock B6.
If your 600 is a 1G, you'll change the looks a little with the airbox gone and riding in heavy rain can cause some water to get sucked in which will lower performance and possibly make it miss/cut out (depending on how heavy the downpour is. The 2G hides the pods behind the sidecovers, so rain doesn't bother it until you feel like you should be wearing a snorkel as part of your riding gear. Of course, if you modify or remove the 2G's sidecovers, you will experience similar negatives to the 1G.
