As already stated, the lowest end (current generation) GPU that supports SLI is the GTX 1070. In order to help you pick the right card, would you mind finding out the full and accurate specs? i7-6800K cannot have DDR3 memory. Also the i7-6800K just came out and is most like your friend's CPU. In addition to the full specs, also please find out the manufacturer and model number of the power supply. If you open up the case, you'll see the mfr & model # on it's side. So your budget is 600 AUD. Which site do you play to purchase it from? Your game in 1080p resolution? Could you name two or three games that you plan to play, to get an idea of the graphic demands.