I'm tossing up between the GTX-980 SC 'traditional' single fan model and the ACX cooled model, running in SLI. I will likely run the GPUs at stock clocks or a very mild overclock, if I go ahead.

I am well aware of the superior cooling performance using ACX with good case airflow, but I am also aware that ~half of the exhaust air using ACX cooling gets dumped back into the case, whereas the single fan exhausts pretty much 100% of the heated air out the rear of the case.

Clearly case airflow plays a significant part in the decision, however I am not sure whether I should go with ACX or not because of my setup... I have much of the internal air from the case exhausting out through a 240mm radiator (Corsair H105 CPU cooler) which cools an overclocked i7-3930K CPU. If the GPU rear exhaust is cut by ~half using ACX, and additionally half of that heat dumps into the case instead, and the only way out is via the radiator, is that going to cause significant heating issues with the CPU, and possibly the GPUs with too much heat build-up inside the case???

I would appreciate input from those who have experience with ACX cooling, since I have never used an ACX cooled GPU myself.


More details about the setup, if required:

Case : Mountain Mods U2 Horizon with a horizontal motherboard tray. All case fans are CoolerMaster R4's.

Intake :

 - 3 x 120mm intake fans in a row at the front of the case on the upper half of the face, which blow directly across the horizontally mounted motherboard.

 - 1 x 120mm intake fan mounted inside the HD bay on the front of the case on the lower half of the face, below the level of the motherboard tray.

Exhaust:

 - 1 x 120mm fan exhausts out the back of the case underneath the motherboard tray (in a direct line with the HD bay intake fan at the front).

 - 1 x 120mm fan inside the PSU which is also mounted underneath the motherboard tray and exhausts out the back of the case.

 - 2 x 120mm fans exhaust through the radiator and out the side wall of the case. Radiator is mounted in the upper half of the case by the motherboard.

 - 2 x GPUs exhaust out the back of the case (or partially inside the case if I use ACX).

Basically the lower HD bay intake fan is exhausted through the lower rear exhaust fan and PSU exhaust, leaving the 3 upper intake fans being exhausted through the GPUs and the radiator only.
 

Thanks.
 
 

 
There is no fan in that rear 120mm hole by the CPU, just a grill.. perhaps I could add another fan there.
 

My case/setup is similar to yours except I have a 200mm exhausting through the top of the case. I get a 7c temp drop using ACX coolers.