A well known overclocker "Shamino" posted a record breaking overclock on the XtremeSystems Forum, What he achieved is an 1500Mhz + Core Clock on Asus's DirectCU Variant of GTX 580. The card was overclocked to 1519Mhz by the overclocker setting a new record for the highest overclock on a GTX 580 card.

The overclock wasachievedusing LN2 as Air Cooling wont besufficientenough to handle the thermal loads. The voltages of the card were pumped up real high to 1.5v with 2.12vdimm and 1.35vpll. Shader was set at 3040 while memory clocks remained at Stock. The DirectCU variant of Geforce GTX 580 already comes with a Factory OC of 782Mhz which makes the overclock almost twice as much as the stock clock of the card. Check out some pics below of the rig in action:

This is the card used:

Source