How much should I overclock my Geforce 1070?

Im kinda worried because my power supply is only 500 watt (its a corsair). Havnt had any problems yet though and supposedly the 10 series is power efficient.

Anyway, as of right now, my GPU hovers around 55 degrees under load (playing a demanding VR game, DCS). I would like to get more performance out of it.

The rest of my system is as follows

i5 3570k @4ghz 8 Gigs ram

I have no experience overclocking video cards at all, only CPU. Whats a good first number to shoot for?