Please tell me how you're getting flash synch at a 250th when max synch speed for a 6D is a 180th? If I fire mine at 200th I catch the shutter.
Cool shot by the way.
I'm shooting with Flashpoint strobes (Rovelight and the older 620m) and using YN622c triggers to hyper sync. This shot was at 1/1250th and I've gone up to 1/4000 without any issue. Works like a charm and have done it for all of my dance sessions in studio.