I still remember reading that you don't want nands to be kept cool.
The controller yes, but the nands you want a little on the hot side.
You want hot NAND when writing to it but if it's hot all the time, long-term data retention can suffer. Regardless, if the controller is throttling you can have a massive performance hit far more than any cold NAND would cause.
All this talk of temperature prompted me to check my 970 Evo Plus (Gen3), and it turns out it's an absolute furnace. 55c-59c idle and easily hits 60s just with light browsing and desktop work. I can't even finish a single run of ATTO without it throttling to half speed.
GPU/CPU idle in the high 30s and that's with fan-stop on the GPU and idle CPU fan speed, so it's not a case or ambient problem.
Multiple people online are reporting the same issues. I ordered an el-cheapo heatsink so I'll see how that goes.