I am having the same issues. Here's my case:
I can stay in crowded areas for a long time with no crash, but cannot join WP Instances without crashing at least 2 times. Other instances make me crash a lot less. The computer just freezes and I have to manually restart it. I get no memory dump or anything like it. No error or system messages. Just freeze, restart. Nothing less, nothing more.

My specs:
I7 2600k, Corsair 8gb Ddr3 1600, GTX 570.

About the temperature, I'd say it's probably not it. Nvidia states that the max temp for this card is 97°. With the max settings, my gpu gets to 80°. With the lower ones it doesnt go higher than 59°C. With both settings I get the same crash.
I've done a lot of things like installing older drivers, capping FPS, reinstalling the game, but nothing really helps it.