You have a revlimiter... Should be between 7 and 8.5k ish. It might not buzz anymore, but it should still be there! An o2 bung really isnt that diff to get going, and if your doing a plug an play, id throw a wideband in it, so you can see whats going on as your riding around. Any of the upgrades you listed will work just fine, just go with which ever one is easier for you to use/understand.