You NEED to set the XMP profile for the ram or set them manually, DON'T leave them on auto in the bios.
Try these settings once you've done that, then test with Intel Burn Test, it's a lot quicker than Prime and will stress the CPU more giving a better indication of how stable it is.( I can run @ 4.6GHz with that vcore 1.312v, so you should get 4.4GHz unless your chip is very vcore hungry)
Once you've found a 24/7 you're happy with you can run Prime for 8 hrs to test long term stability.
If it passes IBT with these settings you can lower the offset by 0.01v and re test until you get a fail. Then raise it by 0.005v, that should find your lowest possible stable vcore.
Using offset is MUCH better than manual as it lowers the vcore at idle.