Sod it, bought the X470 Taichi Ultimate. I'm sure 10 GbE will be far more useful to me than PCIe 4.0 over the next ~5 years, and everything points to older chipsets not hindering CPU or RAM overclocking at all compared to X570. I believe AMD officially said something vague about performance not being affected at least, plus X570 isn't designed to replace X470, it's more of a new tier being added on top.
It's a great board for ~£230, it will be hard to beat with an X570 in price to features/performance.