There is no exact voltage that you set, it differs from one card to another, there will be similar voltage but not the same. It depends on your rigs you will be the one who will find out what voltage is suitable for your system. It`s an experiment that you will do and we are only here to guide.
Having 80FPS in BF4 is an understatement for FPS drops within chokepoints of the game (chokepoints=scenes having intense graphics).
60FPS is the ideal and beyond that is for high end gaming/resolution.