What's fucking me up today is Noctua does not list the temperature in which their MTTF is rated. By comparison,
Corsiar won't give you any expected lifetime, not surprising.
I found one Artic fan that did have a lifespan listed, one that did not (P8 Max and P8)
Meanwhile in the industrial world:
Nidec just gives you an expected lifespan
Sanyo Denki will give you lifespans at 40c and 70c operating temperature.
Delta, well, Maybe give this a read.