No OC on those Intel mobo's worth anything, be lucky to get 4.1-4.2. Intels run a safety gizmo that kills OC if it decides the current is too high. And it's not changeable. So you get stuck trying to get the highest multiplier at the lowest voltage and minimal current which ends up at 4.0-4.2GHz and just over 1.2v
Nothing runs on single threads anymore, most games are at least 3-4 threads and any online multi-player game like fortnite or WoW is going to run more.
And no, the i5-3570k does not have single thread performance better than an R5 2600, in fact it's pretty much the exact same IPC. So considering the differences:
I5 - 4 thread, ddr3, low multi-core performance, max speed 3.8GHz, EOL dead tech, replacements on ebay, good luck there.
R5 - 6/12 thread, ddr4, high multi-core performance, max speed 4.0GH+, upgradable, replacements new with factory/vendor warranty
Still can't figure how its a bad deal and keeping 7 year old tech is a better decision. Single core performance doesn't mean much anymore and should not be a basis on which to decide outcomes. It's not gospel and is only to be used to compare cpus, not as a criteria.