I'm sorry if this has been asked before, but I can't seem to find any solid answers. As you all know, the Modu82+ was well reviewed here as a very quiet PSU. I'd like to purchase the 525W, however it is unclear if it will have the same "noise to wattage" threshold as the 625W. There's quite a price premium between the 525 and the 625 so I'd like to get some feedback how quiet it is.

There was an article at Anandtech, Debunking Power Supply Myths, and this page (bottom) may have the information you want:
http://www.anandtech.com/casecoolingpsu ... i=3413&p=6

Wow, that's exactly what I needed to see. Thanks!

According to the graph, the noise threshold will be the same up until about 250W on both Modu82+ PSUs. However:

The Modu82+ 525W fan starts to ramp up around 250W.
The Modu82+ 625W fan starts to ramp up around 310W.

For me, it's probably worth the price premium of the 625W. I'm currently running a Seasonic S12+ with a slightly noisy fan, i.e - slight clicking noises when my system isn't under load. I have to RMA it but will likely give it to the wife.

Anyhow, the Modu82+ 625W would give me more leeway for power hungry passively cooled videocards, such as a 9600GT. As I'm running my E8400 Prime95 stable @ 4Ghz (with a Zalman CPNS9500 < 5v!) but I'm currently limiting myself to a HD2400 due to the low power requirements. This keeps me under 250W on my current PSU, which also increases in noise past that..

I do use a Modu82+ 525W in my dead silent system,
with a (passive cooled) 3870 Sapphire graphics card and a Q9550 quad core clocked @ 3400 Ghz.
This PSU handles the power need easy, the fan hasn't been spin up from the default 490 rpm yet.
Highly recommended.