I keep my GPUs <70° as well, sadly that doesn't protect the cards from dying. My 2080 also died recently, funnily enough, after I send it into retirement (in my second pc). Rendering takes it's toll, especially if you do it nearly every day.
Hdri's have a very specific problem: they don't scale properly and tend to look weird in certain angles, so I'd have to make several hdri's for several situations, angles, camera positions, which doesn't really help speeding up the process. Anyway, I'm good on the hardware side by now, rendering time isn't that much of a problem anymore (though it will always be to a degree).