I had a 120mm Fortron 300w FSP300-60PN(A)PF, the fan controller spun up to 8-9v at a fairly moderate load, it then stayed there and was loud to be fair.
The fan that was in mine was a Yate Loon 120mm D12SM-12 but was a slightly different fan from what we normally see, the fan hub is bigger and is not that quiet at 5v, could be the ball bearing version?
Here's a pic:
So anyway I ran the psu with an evercool 120mm at 5v(~30cfm) wired externally. Air coming out the removed grill was fairly warm. Ran it for just under a year. Was much quieter, but no way near as quiet as my current older gen seasonic 300watter w/ 80mm L1A (never goes over ~5.5v).
I can't guarantee it'll be safe, but mine seemed alright.