I swapped the stock fan on my EVGA ftw hybrid with a noctua chromax f12 static pressure fan. I plugged the pwm fan into a chassis fan header on my mobo. I'm getting odd instability issues when trying to benchmark, and I have the noctua fan set at max speed. My temps are also about 4 degrees Celsius higher than the stock fan... So far I'm not impressed, do I have to have a fan hooked up to the 2-pin fan cable coming off the GPU, is that where my instability issues are coming from? I'm considering a ML or SP fan from corsair, I thought all the hype around noctua I would give it a go, but so far I'm not impressed. I wanted control of the fan because the rad is used as my exhaust fan so I want to be able to control it. I could hook up my bottom 3rd chassis front fan to the GPU fan cable, but is that what is causing the instability? Thanks, I should have gotten a higher RPM fan because the rad is rear exhaust so should be able to move some air out and my very scientific hand test doesn't feel much air coming out even at max speed which I have it set at now. Any tips, suggestions for a more powerful fan, and insight on the instability would be appreciated. Thanks! 
 
Edit: Here's some quick benchmarks/validations
UserBenchMark: 
CPU-Z:  
GPU-Z:  
Here's one from before the fan swap but CPU was overclocked to 4.8 instead of 4.6:  
 
Didn't realize I couldn't post URL's
 

Thanks for the response. I'm not over clocking the gpu, I am over clocking ram to manufacturer approved boost clock, and CPU is a modest overclock to 4.6 from it's default 4.5ghz boost clock. Since this is the ftw and not ftw2 or icx it has a 2 pin fan cable coming off the gpu for the gpu radiator fan which I left unplugged. Could that be causing the firmware/card bios to throttle because It doesn't detect a fan? I know the small temp increase wouldn't cause instability but it was disappointing after all the hype to get cooler temps on the stock fan vs the noctua... Going back to Corsair SP or maybe try a ML fan because I need static pressure and airflow to balance the positive pressure in the case.

Might be air bubble now at the pump from you moving the rad yo install the different fan.

Tip the pc case so any air that may be trapped at the GPU can now move up to the rad where any air should be.

That's all I can think of for the temp being higher now.

virtuousevga
Thanks I'm not getting instability in regular gaming / regular PC use, only in certain benchmarks, namely realbench. In furmark I maintained a stable 60C with a peak of 63C on 4k stress testing with a clock offset of +125MHz and memory offset of +400MHz. So, stable at around 2050MHz, and gained about 8-10FPS from the overclock so not too bad.

It sounds like you don't have a stable overclock.