Received my 2nd hand 28" beauty dish today. White inside. It's a PhotoSel, similar to Fotodiox, a clone of some kind with a Bowen's mount so it hooks to my S-Bracket great. Came with a diffuser sock.
Flashpoint R2 TTL Zoom at Manual 1/1 is producing F2.8 at approximately 5 feet with the sock on.
So judging from that, with ETTL & HSS, I will probably be able to muster around F1.4 or F1.2 at 4~5 feet. Should do it. Barely!
Obviously I would be way better off with an AD200 or equivalent, and I have my 600Ws of course still that is battery, but still, looks like I might be able to actually use this with a speedlite with my fast glass.