I have a 3ghz processor (I know; old) with 8gb RAM and 64-bit. I tried it on a different system (one I don't typically game on), and it seems that maybe whenever the game tries to autosave is when it crashes on my normal system.
Can you please email me specs of both machines (including operating system, video card and video driver versions) and a copy of the game log (from a play session where it has crashed!) to the address under the "Technical help" section here on the store page?
Autosaves are meant to happen every 10 minutes. If it's crashing after 5, I suspect it might be something else - I'll know more once I see a log :)