Hey Wedge

I've just had the same thing happen to me with 2 cards in SLI which were working perfectly for almost an year. What happened was during a (light weight) game not even 10 minutes into it, my PC completely went off.
The way it turned off I thought there was a power surge but it wasn't as the lights were still on. Trying to reboot nothing happened the fans just tried to spin up but the PC stayed off. I removed the first card took a look at it, couldn't see anything physically wrong with it nor did I smell anything. Then I put this card back in, and took the 2nd card out. I tried to boot again this time the fans and everything started spinning and everything seemed normal, until I smelled burning, at which I turned off PC straight away. Checked card still couldn't see anything.

It was late so decided to check the card in the morning, put in the 2nd one to attempt to play just 1 more game...and then it happened again to this card almost at the same point in the game as well (about 10 minutes into the game).
In the morning I finally saw where the damage was, on the top of the card in a similar location to your pictures, were scorched black marks.
My friend let me use his PSU voltage test tool and it showed that the PSU was giving the correct readings....also I briefly ran just the CPU and MOBO (for about 5 minutes) before turning it off again.

Now I am using a second PSU from another friend while I try to confirm what the fault is, currently just my CPU and MOBO have been running in the same way I regularly use them almost the whole day while I work and sometimes in the evening I play the same (light weight) game that killed both my GPU's everything works fine, I have tested a really crappy low power GPU into all the PCI-e slots and confirmed they all work, but I have not played any games on it (using integrated graphics).

I have applied for RMA but uncertain I will get any compensation for the GPU's as the physical damage is obvious when you look carefully at the cards.

Did you ever find out what caused this problem? Was it your motherboard, PSU or bad (and really unlucky) Graphics cards?

Regards

Tiz