My daily 3600 tight timings are stable when I use a fan to cool my RAM, but throw errors when I don't. I would say the errors start coming around mid-40*C.
And RAM is absolutely capable of running at higher temps when left at stock or close to it, but when you push RAM to the edge temp becomes a factor. And since many folks are trying to run their RAM at the very edge the temp that starts to become problematic can be pretty low. So yeah it's anecdotal evidence that points to 42*C, but it's not a rule. Obviously not if someone can run their RAM at higher temps. But if someone is running their RAM at higher temps then they may find some more performance if they lowered their temps.
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