If you go with air cooling on a threadripper, I suggest going with a Noctua cooler instead of Dark Rock. Dark Rock extended the size of the heat plate to match the TR cpu size, but they didn't cover it with heat pipes, Noctua did. Cooling performance really suffers on the 3990X because there are chiplets on the edge of the cpu. the 32 and 24 core models it may not matter so much.
See: https://www.kitguru.net/components/cooling/luke-hill/threadr...
On non threadripper cpus I actually like Dark Rock better. Cooling is the same as Noctua but it looks cooler and was quieter for me.