Typically to calculate the amount of power you will need you take the CPU and GPU max TDP add them together, and double it. You double since most PSU's are most effecient at about 50% load, and the other components have a little bit power draw. The i7 4790 has an 84w max TDP and most nVidia gfx cards are around 170w. If your estimated use is 443w I would go with 500w with high efficiency. The higher the efficiency the longer your components will last.
P.S. Im not sure what kind of draw an AMD card will give you, but it is usually a bit higher than nVidia and Intel.