I'm wondering if you took an H100i GTX and replaced it's fans with the Noctua fans - you should get the same temp results, but with the lower noise.  

 

 

 

The NH-D15, and indeed the "S" variant, use Noctua NF-A15 fans. They are actually 150mm fans, with a 140mm mount. So no, I don't believe they can be installed on a H100i that accommodates 120mm fans.

 

You would be looking at something like the Noctua NF-F12 focused flow, high static pressure fans for a direct replacement on the H100i. not as powerful as the Corsair fans, but a good balance between performance and acoustics.

 

NF-F12: 1500 RPM. 56 CFM. 22.4 dB. 2.61 mm H20 Static Pressure.

 

H100i fans: 2700 RPM. 77 CFM. dB 37.68. 4 mm H20 Static Pressure.

 

 

The above, clearly demonstrates what I said earlier and in other threads. many AIO manufactures cheat by fitting high RPM noisy fans.

 

There is no free lunch. The Corsair fans are high RPM beasts. It's a balancing act in any system, between acoustics and performance. 

EDIT:

 

I'm a fan of big tower coolers as you know. However, If you are set on AIO and you want the best balance between noise and cooling, then a big rad is the way to go. If it were me, and I was going AIO, I'd go for the H110.

 

Bigger fans cool better for less noise, and greater surface area in a heat sink or radiator results in lower temps.

Martin,

 

Thanks again for the all the input!  You've given me a lot to think about and I haven't made up my mind yet.  I'll pop back in if I think of additional questions!