nothing you can do in software can hurt the card in a way that is not covered by warranty.
Basically you can raise all 3 (temp, voltage, power) limits to the max because:
1. the card constantly monitors itself and will lower whatever to stay within safe limits.
2. the power limit if funny. there is a power limit and power target. the later is significantly lower than former. and the card will try to meet the target.
though from my experience that will not give the best result.
playing with the custom voltage frequency curve is more complicated, but more efficient. I was able to achieve max overclock at 1.05v as opposed to 1.093v max.