I'm looking into my options for high-output studio flash units. I'm interested in which units are the most efficient, so that they really do put out something resembling what their watt-seconds suggest they do. For example, I know that the Speedotron BlackLine 48xx series has a guide number 50% higher than the 24xx series. Does anyone know where I can go to get this information consistently, to make an informed decision about lighting equipment? It seems like most manufacturers don't want to put out comparable information so you can't shop their equipment on meaningful comparisons.