I'm not sure what exact driver you have, ddeck, but you can find the specifications for your driver on google.
Here's a screenshot of the expected lifetime VS case temperature for a random 600w inventronics driver.
It's also difficult to say what exact temperature your driver will reach as it is dependant on the temperature of the air around it, as well as the airflow and how close it is to other warm objects, such as a heatsink and PCB.
Here's a thermal test we did not long ago.
Our lamps are designed to stay below 50c/122f at full load in a 25c/77f room with no air circulation.
Placing a driver on the 50c/122f warm PCB will result in
60c/140f+ temperatures.
Hanging the driver in the air freely results in just below
50c/122f temperatures.
The PCB was also 6 degrees celsius warmer right where the driver had been mounted.
This is why we have our driver hanging freely instead of having it mounted on the lamp.
All drivers work differently and reach different temperatures in different grow spaces, but it's always wise to try keeping them (and the lamp) as cool as possible.