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I haven't been mining for very long but having gpu fans to 70%, undervolting, underclock shouldnt be too bad on the card. Running long hours in high temps causes wear on the components. Fans spinning really high can wear them out too. But if the fan goes you can replace them.

If you're limited on resources it's best to be cautious and make passive income rather than greedy and maxout your card. Don't make gpus cry