Now I have a question for you. Someone tolled me that if I overclock my cards I need to increase the voltage. Even if that is not necessary for stability. You just need to or you will damaged it. Is that right? It sounds wrong to me but I'm no expert...
If you are stable, then there is no need to increase voltage. (You might have some issues that don't cause the card to stop working completely that require more voltage however.)
It will definitely not ever do damage to run at too low voltage. Running at too high of a voltage is where you might do physical damage to your cards.