After several hours of running with a Scythe Gentle Typhoon AP-15 (58.x CFM), I saw a performance slowdown of roughly 8%. While I had thought the airflow coming from the front of the Cube was similar to the stock fan, it was noticeably warmer air coming out.
So, I used twist ties to attach another fan to the front. The result is hideously ugly, louder, but still much quieter than the stock fan, and is definitely putting out more air flow. It still feels warm, but I'm not using thermometers to measure this stuff.
There is also zero back flow out of the back where the fan is supposed to go. With both the stock fan and my Scythe replacement by itself, I was getting some back flow.
So far, my missing performance is back.
I'd appreciate anyone's insight on all this.
Using a wind meter, I just checked the velocity of one of my cube fans... It's showing about 20fps, or 40CFM. So not the best fan's in the world to begin with. I am not having any heating issues, but I've installed my cubes into some datacenter space where the ambient cool air is ~65degrees. I wanted to check the air volume so that I could gauge what level of fan I need to upgrade too since I am about to flip the fans around. I thought everyone might find my results interesting and/or helpful.
If you have your cubes installed at your home, it's likely the ambient temperature is more like 70 or higher degrees. This would then be just pumping warm air over hot heat sinks so doubling the air flow would almost be completely necessary since it'll dissipate less heat as the air passes over the blades.