It's times like this when I wish I had an IR camera; I have some of those 3W leds, and I've driven them in still-air at 1W without any heatsink or star carrier as in the picture. I had them running like that for about an hour. They were much too hot to touch but I have no idea of their actual temperature.
There was no brightness change, and no "hot smell of silicon", so I think they were OK, and they still work now, but I admit I was running them blind. But at just 33 cents each, I didn't care at the time.