i'm looking to get my first flash. i need it because I'm shooting an event at a club / bar next week. my ultimate goal is to use the flash off-camera with a stand and umbrella (i.e. strobist), but there will be situations where it will be on-camera as per necessity. So I know that I would eventually need the canon wireless trigger (which is like $225) in order to use the flash remotely. What are the main differences between the 430 and 580? and what would be the advantage of one over the other based on my requirements? thanks!!! i appreciate your help.