Below is the modified build with a dedicated GPU: The
Asus Strix GTX 970 4GB factory overclocked A$ 465, the 980 (A$ 650-825) and 980TI (870-1100) are above your allotted A$500. But since you dont have heavy gaming in mind the 970 is more than powerful enough. Last years model. In fact the 970's power was the reason the 980 sold so little.
http://au.pcpartpicker.com/list/YWFsYr
If you rather prefer an AMD graphics card check this list (
R9 390X factory overclocked), but going by your Intel CPU i'd say you're not
http://au.pcpartpicker.com/list/qKvjXH
If you do happen to install some modern games, either GPU will be plenty capable to handle them at ultray or very high. If i'm right either build should save you about A$ 500 between what you chose
If there's anything else, just give a holler