An overclocked RX570 will never match the performance of an RX 580. An RX 580 should be nearly 15% faster than an RX 570 in graphics-limited scenarios, whereas overclocking a graphics card will typically not give you more than a few percent more performance. It's probably not worth bothering to overclocking these cards, as the difference in performance is unlikely to be noticeable compared to stock, but temperatures and power draw will be higher.
Of course, RX 570s tend to cost less, which might be worth considering. I wouldn't pay a similar amount for an RX 570 compared to an RX 580.
If buying new, you might also consider something like the newer GTX 1650 SUPER, as that card is often slightly faster than an RX 580. It only has 4GB of VRAM though, so it might not hold up quite as well in the future. A GTX 1660 could be a good option too though, as it can be over 15% faster than either of those cards, and has a decent 6GB of VRAM.