Here is why you have to be careful, https://www.techpowerup.com/review/amd-ryzen-9-3900x-tested-on-cheap-b350-motherboard/3.htmlThat's a good table, mine is 171, recommends minor airflow if I overclock, to be honest I dont have a single case fan but my vrms idle at 32°C, hit about 42°C under load and very rarely top 50 °C if I'm benchmarking so maybe I'm just lucky.
Note this is a 3900x and the VRM temperature on a B350 motherboard. In this case they used a ASUS Prime B350-Plus .
Let's see what happens when we use a 240 mm AIO instead of the Noctua. This reduces the air flow over the VRM's because the AIO block does not have a fan.
Here, we are playing Battlefield V on the system—things are heating up now: 116°C.
With our multi-threaded Blender load applied, the VRMs reached 130°C, but the system did not crash and chugged on perfectly fine. As we've seen, this seems to be the point where some sort of throttling starts to ensure nothing gets damaged by the heat.
If we overclock the CPU, too, to 4.0 GHz at 1.225 V, VRM temperature goes way above what these coils are rated to handle, reaching 138°C and higher. Once 140°C is reached, the CPU will reduce its clock speed to 550 MHz (no matter how many cores are active), which immediately drops the VRM temperature well below 140°C.
This is what they mean by keeping air flow over the vrm's. From our spreadsheet row 162 we can see,
|Prime B350-Plus||ATX||🗙||＊＊||＊||✔||4||1x 4C09B||2x 4C06B|
So the spreadsheet tells us we must keep major air flow over the VRM's for a 3900x. That installing a 3950x is unwise. Above the AIO provides none of the air flow an air cooler would provide causing the VRM's to overheat.