Well, I went out to test the range of all 6 of my Yongnuo flashes and triggers yesterday afternoon, but misjudged in my mind just how far 300 meters is. I figured I could do it right out on the road next to my place that runs down to the river locks, but again, misjudged it.
I got as far as 120 yards per my laser rangefinder, which is about 110 meters, and they were still all firing just fine. Then a curve in the road kept me from being able to see the flashes to see if they were still firing. Next time, I'll get out on the main road, which is nice and straight for miles, and do a proper test.
For now, I'm happy with the fact that they fired flawlessly and without a single failure all the way out to 120 yards, which is about the length of a US football field, including the end zones. According to the manufacturer, the range is 300 meters, so I'm eager to see how they stack up to that claim, not that I'll probably ever use them even as far as what they achieved so far.