I have been using a 430EX II on my EOS 7D and EOS 5D Mark III, most often with a Gary Fong Lightsphere, for indoor or outdoor family events or weddings. I am rather happy with it but I am questioning myself whether the more powerful 600EX (with a guide number of 60 vs. 43) would bring any benefit for this kind of usage?
One of the particular aspects where I found the 430EX II to be limiting is the recycling time, e.g. for repeat shots such as when the new weds walk down the church's aisle. But if I read the technical specifications correctly, the 430EX II has a recycling time of around 3 seconds and the 600EX would take even longer with 3.3 seconds (source: Canon's official website).
Any real life experience with the two Speedlites?