OK keep in mind that I use Precision to set my over clock but my below specs are from GPU-Z validation.
At stock Precision or you can use Afterburner reads 797/1594/2025 but GPU-Z reads it as it should be which is 797/1013/1594. So the Shader clocks are different when you over clock them to the actual value GPU-Z reads them. So use both your over clock software and then GPU-Z TechPowerUp! software to get your acurate reading. If you go to the 'validation' tab and hit 'Submit' button you'll be directed to a validation page which will tell you exact percentage of over clock.
My default voltage is 1.0872v. I found out that default voltage can vary from GPU to GPU. I was always wondering why other people would get lower temps than me at stock core default voltage. I currently lowered mine to 1.0750v which brought down my temps by 1C and still run stable at 875/1111/1750 24/7.
Here are some of my 580 SC clocks to help you. All voltage on these were using my default 1.0872v.
The GTX 580 SC is 3% gain higher than a GTX 580 vanilla at stock speeds.
39-40C idle @ stock 797Mhz core on SC which is a 3% gain over vanilla stock.
40-41C idle @ 838Mhz core on SC which is 8% gain over vanilla stock. 838 Core/1061 Memory/1676 Shader
41-42C idle @ 855Mhz core on SC which is 10% gain over vanilla stock. 855/1086/1710
42-43C idle @ 875Mhz core on SC which is 13% gain over vanilla stock. 875/1111/1750
43-44C idle @ 890Mhz core on SC which is 15% gain over vanilla stock. 890/1135/1780
To go higher stable I have to bump my GPU to 1.1000 voltage.
44-46C idle @912Mhz core on SC which is 17% gain over vanilla stock.
Now when I OC I bump up across the board for Core / Memory / Shader to be exactly the same percentage gain on each GPU-Z validation.
I got clocked to on my final score 3D Mark 11 mid level performance score of 6902. On an i7 950 @ 3.8Ghz OC - GPU 1.1000 voltage @ 912Mhz core.
3D Mark 11 score of 6902.
This card can go higher but to be honest I'm not comfortable going higher. These are safe values for my card. Keep in mind that cards over clock will vary card to card. Some cards go higher where others can't, it's just luck of the draw. All however work at stock clocks as they were made for with warranty.
Welcome to OCN btw and hope my homework and over clock chart I kept helps you.