LtDave.
If wanting a “Studio strobe” for more power, consider the Westcott FJ system. They will work with the “Radio Communication” from your Canon ST-E3 RT Transmitter. E-TTL, Manual or Group Mode, your choice. You could put an FJ 400 or 200 in your 7ft. Umbrella and then use your existing Canon 600 EX-RT Speedlites with both the Canon and Westcott all in Radio Communication. One 600 as a rim or edge light and the other to illuminated the background.
It’s not an either or system but an integration.
More options and more flexibility.

