As mentioned prior, every silicon IC is different. Manufacturing processes guarantee that difference. There'll be different levels of impurities and contaminants in every chip, it's unavoidable. That affects exactly how any single IC behaves, it's timings, resonances, amperages, power delivery etc.
There's not just one chunk of silicon in a gpu, there's a couple dozen. To guarantee stability of the gpu across the entire manufactured model, speeds are set low, voltages are set high. This gives a very wide range of compatability that covers all the silicon, no matter which particular card or combination it's on.
That's where OC and UV come in. Since AMD is not about to fine tune every single card, it'll be on you to discover just how much more speed the silicon combination can really handle and stay stable and just how much higher the stock setting is as compared to what your silicon combination really needs.
Ppl have called OC and UV free performance boosts, in a broader sense, that's not true. The performance was always there and when buying the card, you paid for it. It'll be up to you to choose whether to see just how much performance is available above stock or not.
Amd, Intel, nvidia they all guarantee a minimum level of performance per card. Anything above that is pot luck. Silicon Lottery.