One thing I have found with the Ryzen 3600XT which I didn't realise before is that it's temperature fluctuates a lot, even when not doing a lot. At first, I thought the cooler might not be mounted properly as I had never seen idle behaviour like this before with my old Intel CPU. However, apparently this is normal operating practice for the Ryzen CPU, as it constantly wakes up cores or something like that. For reference, when I start the PC and go into the Bios, the temperature is low 30s. Once fully booted and in Windows however, it can keep going into the 40's and 50s.
You say the peak temperature is 72c, but what is the average? I will hit the peak of 70c every now and then, but the majority of the time I am in the low 60s. Those are perfectly good temperatures for a CPU in my books and, as you said, it is a lot quieter than the Wraith Prism. The 3600XT didn't come with a cooler, but I would properly still opt for the Mugen just for the reduced noise alone. I am guessing your plan for a Noctua U9S Chromax is also now in doubt?
As for GPU temps, they will definitely play a role. With the way the fins on the Mugen 5 are aligned with an exhaust fan up top, it is inevitable that GPU heat is getting sucked up. Hope this helps the thought process, but understand it can be frustrating. I have spent days on my fan curves before realising I was setting the case fans to look at the wrong temperatures!
