I'm glad to hear it works, although with warning. I contacted Canon specifically about the x-sync speed on the 600EX-RT (in radio mode) and the 7D to see if the new 2.0 Firmware would make it work faster than 1/125 and they said no. For hummingbird photography, I can't solve the problem with HSS for 3 reasons: (1) max shutter speed is 1/8000 and I need 1/10000 or faster, (2) HSS flash uses more power (since it's firing almost continuously at 40Khz through front and rear curtain drop) and thus doesn't recycle very fast, and (3) the brighter light startles the birds compared to what I normally use, which is 1/16 to 1/32 power with a shutter speed of 1/250. It would be nice to know what the limiter is on the 600EX-RT for x-sync. Since optical slave works at 1/250, I'm assuming the Canon radio protocol is inherently slower. Since it's a new design, and since after-market radio slaves have had no problem with 1/250 x-sync, I'm kind of surprised that the Canon Engineers couldn't figure out how to make it work.