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.