I recently purchased an AMD setup similar to yours with the R9 3900x coupled with Asus ROG x570-F gaming. I'm using 4.3mhz @ 1.3v with CPU LLC at Level 2 & SOC LLC at Level 3. I'm getting 74 degrees C under full load on CB R20 that's using a Corsiar H115i AIO. From reading so many reviews I'm still unsure on the best voltage to use and if LLC should be used on my setup currently. Still so much to learn. I too have upgraded from an old system, I had a i7 3820 on the X79 Sabertooth which kept me going for years. Curious what bios settings you're using now after having your setup going for a couple of months now?