I'm assuming you mean on all 8 cores?
I have my 2700x under an EK EVO Supremacy block and I played around with some overclocking. At 4.2 on all 8 cores I needed 1.41v to run Intel burn test stable. I really have not played around with overclocking as much since at stock a few of the 2700x cores jump to 4334.
I think there is very limited headroom for overclocking all 8 cores in the 2700x but at stock it runs all 8 cores at nearly 4Ghz which is quite a jump from my 1800x AND the temps are a lot lower.
I ran my 1800x OC'd to 4Ghz on all 8 cores but the stock 2700x is slightly more responsive and scores a bit better in benchmarks.
Temps for the 2700x really jump at 4.2 (all 8 cores) and above. Just not worth it vs stock.
I'm using an Asus CH6H mb with the latest release BIOS 6004. Most likely a premium x470 mb will be able to squeeze a bit more performance from the chip but I doubt much more.
BTW, I jumped to the 2700x because I had @$325 in gift cards. I'll repurpose the 1800x.