... the flash duration at t0.5 is 1/2100. Based on that, can I assume that at t0.1 it is around 1/700, and is that good or bad?
...However, I also applied what's sometimes known as the "HSS hack": I had one of my Cactus V6 II transceivers on the camera's hotshoe with the other connected to a regular flash (nikon sb800 in my case). I then ran a sync cable between the flash and the studio strobe, and that did the trick.
... It's not 100% though, as not the entire frame was evenly lit. I'd say it's about 90% there.