Conservative OC for GTX 560 NON TI SLI

http://www.newegg.com/Product/Prod [...] 6814127592

I have 120mm x2 rear and bottom mounted fans. 200mmx2 top and front fans. CM Hyper N520 HSF. Storm Sniper Case. Running GTX 560 NON TI SLI, idle temps are around 30-31, on load via 3D Mark was around 72 max for GPU 1.

I want to very conservatively overclock my cards to get the most out of it. I had heard that 900mhz at 1.07 V was a good starting point? If I did this to both of my card what kind of performance would I be looking forward too? Would my SLI GTX 560s on 900mhz beat a GTX 580? Is my version of Afterburner up to date? Thanks!

Left the Voltage the same, raised the core clock to 850, and fan speed to 40 on auto.

Ran Unegine Heaven 2x
Ran 3D Mark 11 Basic Performance Test

Idle temps: 35
Max temps: 67

Before OC Scores:
Heaven: 1631
3D Mark: P7326

After OC Scores:
Heaven: 1693
3D Mark: P7582

Is this too conservative? Should I got further?