Noctua says the NH-9Ls are for up to 65W TDP for AMD but has a qualification that leads me to believe that I could use it with the nominal 100W TDP 5800K which idles at about 43W. The qualification is here:
http://noctua.at/main.php?show=nh_l9a_tdp_guidelines
and reads
The SPR NH-9Li review used an overclocked 95W CPU and did quite well.3) Our recommendations assume that the fan is used with PWM control (configured so that it can speed up to 100% when necessary) but without the supplied Low-Noise Adaptor. If you would like to use the NH-L9a with the supplied Low-Noise Adaptors, we recommend choosing CPUs with less than 65W TDP.
I will be building a new system. I live in a relatively cool climate so meet the below 25 degree C ambient guideline. I am thinking of using the Silverstone Temjin-TJ08E case with excellent cooling along with an ASUS F2A85-M Pro MB.
If folks think my idea is too risky, not likely to be quiet, etc., please suggest an alternative cooler.