neuroanatomist, thanks for correcting my claim.
I want to apologize to the forum for posting something based on belief, not fact. When I made my claim yesterday, it was based on what I thought I remembered happening, as I was traveling light and did not have two 600ex-rt's to test before typing my bologna.
Canon Professional Services did, in fact, believe as I did, that the zoom head of a slave could be controlled from a master 600. When I fill out the latest feedback info, I will very politely point that out to them.
So I came home and, spurred by neuroanatomist's post, verified that he is correct with a simple series of test shots against a wall.
In the future, it would be great if Canon could figure out how to control the zoom feature from a master, but I realize now that any changes made, say for power or mode, are apparently transmitted when a shot is taken, not before. Since changing the zoom takes a few moments for the mechanism to adjust, making the change can't happen simultaneously with the shot.
So, I'm done hyperventilating on this issue and I will keep my st-e3-rt, which did work very well at the event I attended yesterday, despite not having the imaginary feature.
Cheers, all, and thanks for posting so much accurate stuff and catching the mistakes quickly.