These are not my results but my clients, who had forced me to make his WS on Dark Rock 4 Pro
A true client from hell :- )
Using "Dark Rock 4 Pro" as example of reference Air-Cooling skews thing negatively for air-cooling Threadripper, (DR4P) it's the only sTRX socket air-cooler which has horizontally running heatpipes across heatspreader, i.e they only cover the four middle dies. It makes sense, it was designed at 1st generation of chips, still, Noctua made correct design decision at same time..
Dark Rock 4 Pro was never a suitable cooler for 3990X, it does somewhat work for 3960X & 3970X because those have dies in middle of the chip. Which is also why those can be very well cooled by any generic Asetek AIO.
The difference proper TR4 air-cooler like Noctua UH-14s TR4 and Dark Rock 4 Pro on 3990X is simply massive.
Just a reminder, these two coolers had
delta of 20 C already with past-generation 2990WX, the first chip with dies that were spread across the full chip.
I've put 3990X under OptimusPC water-block, state-of-art block that is even 2-3C better than the previous winner, Heatkiller IV. After that, it doesn't matter how many radiators it is connected to (in my case 2x420mm) since the issue is heat-transfer from chip, not dissipation from the loop. At room ambient of 25C, the effective boost clocks on long renders are effectively identical between this build and the one with Noctua UH-14s.
That obviously very quickly changes with PBO/Curve Optimizer/Static Voltages/etc.. (any other OC technique), where loop or even the funky tower from Ice-Giant pull quickly ahead, by a large delta. Past 280W (and it's not hard to take 3990X into 700+ W territory), Air is no longer viable.
99perc. of users on this forum are running their PCs stock. That's matter of life for most workstations (discounting XMP/DOCP profile).
Ultimately, my personal suggestion comes down to budget. If you can afford 3990X, get it, even if it scales very little in certain workloads, or particular working conditions.
3970X might indeed be more prudent, more universal option, it does maintain better boost clocks with simple math of diving its 280W power budget only between 4 Dies + 1 MC, a benefit which is partly negatively offset by worse cooling (4 centered dies are harder to cool than 8 spread-out dies).
TL:DR :
Buy the one you won't regret spending budget for.
If you have sizeable render-farm, your choice is more partial towards 3970X. If you have only single-workstation that acts as your main rendering machine as well, absolutely go for 3990X.
Air cooling is absolutely viable, zero-issue choice for 3990X. But you have to choose either Noctua NH-U14s TR4, or Ice-Giant. You can ignore the existence of everything else.
Few graphs to show how much Dark Rock Pro 4 sucks, and why it should never be used as argument against air-cooling Threadripper.
Also article from KitGuru that explains the failed design of this cooler.
https://www.kitguru.net/components/cooling/luke-hill/threadripper-3990x-cpu-cooling-comparison-how-to-tame-the-beast/11/
