I would 100% recommend the Noctua-NH-D15S which fits perfect to the first pci-e slot on most/all asus mobo's!
Best temps, best build quality and easy to install (got 6 or more coolers from noctua in the past).
BUT:
If you want real low temps you need to delid your cpu:
My 7980XE had on two cores a max temp of 86 degree.
After delid the cpu & Conductonaut (with noctua) the temperature was max. 59 degree (@ 30 degree room temp!!)
Tested with 1 1/2 hours Aida64 stresstest.
If you want to see my pics:
https://www.computerbase.de/forum/threads/delid-die-mate-x-heatspreader-guillotine-fuer-skylake-x-un...