This game kills my machine in a way I don't think I have seen before: computer stops responding and I lose video signal (not just black screen, but really no signal). Happens every few hours of playing.

This is on Win7 64 with Radeons 6870 x2 crossfire, i5 2500k and 8GB RAM. Running 1920x1080 full detail.

Has anybody experienced anything like that?

I have a somewhat similar system:
Win7 64 with Radeon HD 5670, i5 661 3.3GHz and 4GB RAM. Running 1920x1080 full detail.

And a somewhat similar issue:
Every few MINUTES the graphics freeze for a few seconds, then the screen turns black and then the game continues as if nothing happened. I've seen it rarely in some other games before, but here it happens every few minutes, which is rather annoying.

This probably doesn't help either of us, but misery loves company...

What you describe is the video card "crashing" and restarting, but without killing your system. Hard to say why it does that.

In my case I am almost sure now it's because the card is overheating. GPU-Z shows it goes up to 100 Celsius and fan 100% speed.