Actually, I'm pushing the temperature limit on the high end by experimenting with them in fully enclosed fixtures, which is something many brands tell you not to do. In the worst case I've burned out two LED bulbs with less total hours on them than you would get from one conventional incandescent bulb. The current bulb is rated for 120° F, but I expect it's engineered with some headroom, so maybe 130° F. We'll see...
Heat will ruin the LED elements themselves primarily through ion migration, which is normal, but heat speeds up the process exponentially. There are other factors but one thing to keep in mind is that LED elements are sorted by efficiency. To meet x lumen output requirements you have to drive the inefficient LEDs harder which produces more heat on the chip. They get sold off to make the cheapest bulbs.
