16 plots starting at the same time is maybe a bit much. For optimizing plotting on that machine:
If you get high cpu temps with a 360mm AIO…something other than Chia is wrong. My first guess would be a bad contact between waterblock and CPU, did you try reseating the waterblock? Is the pump running?
Aslo some motherboards can have really high CPU voltage settings out of the box that causes it to run hotter than it should
Edit, also 7500MB ram is overkill, I think the max recommended is 6750 or something like that but anywhere between 3600 and 5000 is plenty