Just to provide an update for this... Ended up grabbing a 5800X3D myself and have done a bit of testing.
Motherboard is Asus Strix B550-I running BIOS version 2603 (Agesa 1.2.0.6b), and the CPU is cooled by a 47mm Black Ridge with a Noctua NF-A9x14 fan swap in a Sliger SM550.
- Setting Package Power Limit in BIOS, as described by the reddit comment I linked above, did not work for me personally. CPU did not acknowledge the limits, and hwinfo did not even see them.
- Voltage offsets were available to me in BIOS, but I haven't touched them (yet?). May only be an Asus thing though, since every time I've seen it mentioned by others, it's been on Asus boards.
- I have however been able to successfully set PPT, TDC and EDC under AMD CBS > NBIO Common Options > XFR Enhancement > Precision Boost Overdrive by setting PBO to manual. Upon stress testing in Cinebench, the 5800X3D strictly adhered to the limits I set, no matter what.
I can't confirm it works on all boards, but I've seen comments saying it works on various Asus and Gigabyte boards at least, and maybe ASRock. Yet to see anyone confirm whether it's possible or not on MSI boards though.
- I haven't tried Curve Optimizer yet, but I'm yet to see anyone say the PBO2 Tuner tool from the overclock.net forum didn't work for them, so that's promising.
I did a few quick multicore benchmarks in Cinebench R23 (which doesn't seem to benefit from extra cache?) yesterday to test how PBO limits impacted the performance and temperatures:
- Dialing it in to match a 5600X (88 PPT, 60 TDC, 90 EDC, so basically ECO mode) got me a max temperature of 74.6 C while hitting roughly 91% of the score of stock values reported online (13,603 vs 15,000-ish)
- Highest score I got without throttling was 14,388 (96% of stock) with 120 PPT, 75 TDC and 110 EDC, and capping at 88.5 C.
- Found my sweet spot at 120 PPT, 70 TDC and 105 EDC, with a max temp of 82-83 C and a score of 14,300 - 14,350 (96% of stock).
The actual, realistic performance hit with extra cache taken into account is probably less though, and in the single core benchmark I was within margin of error of stock scores no matter my values, while only hitting 64.0 C at max.
I'll see if I can get the chance to a bit mess around with Curve Optimizer via the PBO2 Tuner tool over the weekend, and what kind of improvements I might be able to get with it.
(Note, this is my first Ryzen chip, my first time doing any tweaking to a CPU and my first time benchmarking, so bear with me)
TL;DR: Setting PBO values on the 5800X3D works on my motherboard and improves thermals enough to work comfortably under my 47mm cooler without too big of a hit to performance. Also possible to manually replicate ECO mode. However your mileage may vary depending on your motherboard.