So Im aware that I have limitations with my cooling and motherboard VRM's, so enabling PBO will probably make no difference from where Im at currently. But if a person has a top line board like the Gigabyte Master or Extreme, combined with a excellent custom water cooling solution, in theory if they enable PBO in those two locations, they should be able to go beyond the 4600ghz of the 3900X up to 4800ghz?
Wrong. I mean, your theory sounds correct even by AMD's documentation. However, as I said, these CPU's are limited elsewhere. The motherboard's TDC, EDC and PPT values aren't what hold them back. Using the motherboard values or even inputting your own makes no difference. I've tried this on the MSI MEG X570 GODLIKE, which while not quite as good as a GIGABYTE Aorus Master in the VRM department, is more than capable of pushing enough voltage to these CPU's to handle significantly higher clock speeds and power than we need even overclocked. In other words, it's not VRM temps that are the problem.
If you watch these CPU's in real time through Ryzen Master, what you'll see is that in order to boost to 4.6GHz, the CPU will pull over 1.5v just to hit those clocks on a single core. Keep in mind that generally speaking, you only see one core that's capable of hitting the advertised boost clock. So, what's limiting these CPU's? I think its a matter of thermals. Essentially, these CPU's are at the very edge of what the silicon can do in its current form. To hit the advertised boost clock requires a great deal of voltage. It probably needs even more voltage to go higher. Voltage needs as you raise clock speeds aren't necessarily linear. For example: You get all the way to 4.3GHz on these CPU's at 1.30-1.35v. Yet, a single core reaching 4.6GHz requires as much as 1.50v+. You can observe this behavior for yourself in Ryzen Master. Load up Cinebench R20, and choose the single CPU test. Run it, and watch that one core with the gold star hit 4.6GHz (3900X) or near it and then look at your voltages. They'll spike quite high to achieve those clocks. It's likely that a great deal more voltage is required to push the CPU even a little bit further. At that point, even on water cooling it's likely that the heat becomes an issue.
You can put all the radiator space in your rig you want to. It won't matter. The thing is, you are limited to the single patch of space provided by the IHS and the conductivity of the TIM inside the CPU. Your thermal paste comes into play as well, but even the range of crappy thermal paste to the best stuff on the market is rather small, so there isn't much we can do there. So we are limited by the IHS's ability to dissipate heat rather than our cooling systems. This is why a high end 360 AIO or even an entry level custom loop is probably enough for taking Ryzen 3000 series CPU's to their limits and why guys like me running custom loops can't break this 4.6GHz barrier. LN2 allows you to go further as we've seen clocks over 5.0GHz using LN2.
Essentially, going to higher clocks isn't possible using ambient cooling. It has nothing to do with the motherboard's VRM's and therefore PBO won't help us. The only solution is more voltage, which an ambient cooling solution using air or water simply can't deal with.
No, because even with a decent water cooling setup you'll still be stuck due to the way it scales clock with thermals as you won't be able to bring the temps down low enough. With how little total TDP these chips actually are capable of drawing and the thermal scaling limitations - You're wasting money on some expensive cooling setup if it's for anything more than just the looks of the setup.
There is literally no reason to mess around with overclocking these chips unless you want a specific value forced via manual overclocking, but if you do this you are sacrificing single core speeds...
PB2 is pushing these chips as far as they can safely go, and there is nothing you can do to modify the values that PB2 scales off of.
The only tweaking you can do that will net you real performance gains with a 3000 series build is just with memory.
Well, actually we can alter the values used by PB2. That's what PBO does. It just doesn't help us because those values aren't the limiting factor. On your point about manual overclocking, I agree and said as much in my review of the 3900X. There is some value to manual overclocking, but only in specific circumstances where greater multi-threaded performance is required and that sacrifice of single-threaded performance is considered a worth while trade off. The types of applications that would benefit from this are going to be the types used often by those using content creation applications almost exclusively. Those people would probably be better served by Threadripper with a higher core count. Essentially, the Ryzen 9 series is in a crossover realm between a gaming / desktop PC and a workstation / HEDT system.
Lastly, in addition to the memory settings, you can also overclock the Infinity Fabric clock which can yield some gains.