Nice review. I can't imagine there are many people are busy building compact systems with this sort of power requirement, but there may be a few customers in the "higher output = better" segment. Even so, I am disappointed with the efficiency of this PSU at low loads, which I think is important to many people building small systems.
Yeah, it's not the best, but it's hard to blame the unit for its power curve, as it's not much different from typical 600W ATX Gold PSUs. I've said this repeatedly -- the only way to get super high efficiency at very low load is to choose a high efficiency PSU rated for low power. But the incentive to make such devices is not high, and the benefits aren't big because the base power is small.
The 450W Gold version of this PSU got a short test in the Silverstone ML05 review
, and it lost 8.7W at 20W load, compared to 11.8W for the 600W Gold. About a 3W improvement (30W vs 33W AC) if your idle is that low. But it's unlikely to be that low if your peak power is >500W, which would be why you'd choose the 600W, and the 450W model wouldn't even be in the running.