After swapping SSDs, tuning fan curves as much as possible, and upgrading firmware for various devices (fan controllers, GPU, BIOS), temps for both drives are just fine. Having a naturally cooler SSD in the top slot really helps. 
 
Extended gaming session. Not too bad.
 

 
But the chipset is still hotter than I would like.. Not sure if it really matters, honestly. The x570s run hot to begin with and seem to be pretty normal around 75c without a heatpipe or other more exotic cooling. 
 
GPU temps plateau at 75C and the drive closest to the GPU only has about a 10c delta between idle and full load. CPU temps continue to be pretty chill.
 
The real question - which temp sensor is the right one to trust? hwinfo shows Motherboard, Temp2, Temp3, Temp4, Temp5, Temp9, under the Nuvoton device, and another rogue "Chipset" temp 
 

 
I don't have a thermal probe, but to the touch, the chipset is smokin'. The number here doesn't seem to agree with the BIOS, but that's hard to test. I assume the "motherboard" temp is the one most people are quoting, but as with all things hwinfo, figuring how to un-gaslight yourself is tricky. 
 
Pretty sure that "chipset" is the "real" one to monitor since the others either decrease as actual temps increase, and the "motherboard" and "mainboard" as shown in CPUID HWMonitor basically never move even though I can tell a massive difference to the touch.
 
Since the original issue is taken care of, I don't think there's anything further here. SSD temps are mitigated down from 80c thermal throttling, and chipset numbers are in the normal range, even though 80c+ on the chipset might be alarming. I have also made a small shroud that blocks the heat from the GPU hitting the chipset, which has dropped temps further by 10c getting down to 70c. Still hotter than some in this thread think a chipset should be, but I think we're all comparing different sensors, so our assumptions about normal are different.