You could do that, but I would be extremely surprised if a 3950X couldn't do 1800MHz IF, especially one manufactured recently. For this very reason, on Asus and Gigabyte boards, setting 3600MT/s XMP RAM automatically dictates 1.10V VSoC as an auto-rule. I don't know why it's not the case for MSI.
As for 3200 and tightening timings, ICs don't exactly work that way. Keeping tCL the same and scaling frequency UP is always easier than tightening tCL below what it's rated for. Hence why 3200 14-14-14 B-die kits exist.
Once you get into higher MT/s speeds, you'll find that DRAM calculator's recommendations on various voltages can be really......broad and optimistic. When in doubt, set VSoC at 1.1V and cut it out of the equation.
Do take a look at your Event Viewer and try to find details for the exact event at the time of the crash. WHEA can report a lot of hardware errors and CPU/Interconnect is just one of many possible CPU errors (e.g. unstable CPU overclock due to insufficient voltage, the dreaded cache errors, etc.).