I haven't seen it throttling when set to 1478 MHz. This is on an Asus 970 Mini with only one 8pins power connector to deliver the juice. You would expect this to run much hotter, as its cooling solution has been tailored for HTPC usage. I could push it even further without any artifacts showing...
Worst PSU I've ever came across! It's fine for about a year, but after that it degrades rapidly. I've had two of these PSU's and both suffered from high ripple/noise patterns which led up to destroying the hardware connected to it.