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Also I don't know why people say undervolt will get more performance, the only thing I can think of is preventing it thermal throttling. And using PBO is technically overclock, not undervolt
With 5000 series PBO can provide a performance improvement when you use something called the curve optimizer. By undervolting slightly when you do that it can keep the CPU cooler and not pull back on boost clocks.
The actual performance improvements seen with PBO isn't very even though. It's generally only seeing it holding rated clocks 'longer', subjectively speaking, with minor improvements in benchmarks. Also, it won't pull back as far as base clock on extreme heavy load. But it's hard to say it's really not as much due to use of really good cooling since one effect of PBO is to raise heat output a lot so you need improved cooling. Ryzen's boost algorithm is so temperature sensitive that if you keep it cool it's as effective as "overclocking" all on it's own.
Thermal throttling occurs when the CPU exceeds safe thermal limits (95C for 5600X) and it pulls clock back hard (something like 800Mhz I think) to allow the CPU to cool off. That's way, way worse than simply limiting boost.
People call PBO overclocking but it really doesn't do that at all; it let's the CPU draw more power and current than specified limits which lets it boost to it's rated clocks longer. The limits (TDP, EDC and TDC) are established as much, if not more, to protect motherboard VRM's. The processor's boost algorithm is left intact and keeping the processor within defined, safe, limits of temperature, clocks and voltage (called FIT). The only time that changes is by increasing something called the PBO Scalar setting.