Gigabyte GTX 580 SO (Super Overclock, also called SOC).
Read more about the card here: http://www.hexus.net/content/item.php?item=30204&page=1
My overclocing experience, from memory:
Complete computer crash, vertical lines all over the screen.
Memory has been pushed too far, try upping the memory voltage - might need a more than you think so keep going.
Lots of triangles on the screen, and weird graphics
GPU needs more voltage. Up the voltage and it should disappear. Cool GPU better or freeze it to archieve better performance with less volts.
Computer locks
Heat issue, maybe on the PWM chips. Your GPU isnt willing to go higher under present conditions. Your GPU might be 40C, only but thats still too much for to run stable. Try too cool it harder.
WATERCOOLED
and on OC setting
3dmark 06: link
3dmark vantage: link
3dmark 11: link