I was in the same quest as you when I got those Coguars, but they still were loud. I also tried another stock fan for the push\pull setup. I was able to find the balance between quiet and efficient using the Bios PWM settings and running them at a sustained RPM rate instead of having them throttle. After that I went to using Yate Loon 120mm Low RPM fans and have them full speed, no more RPM messing around. All my fans are now Yate Loon as you can see in my sig, ranging from 120mm to 140mm.
dja2k