i think it's better to go with the 480 4gb, should be at the same price or at least here i'm finding it at the same price
also i don't think you need at all a 1600w, 1000w is enough just buy a corsair rm or evga 1000/1300(if cheaper some times)
rm 1000i is very cheap can be found at 170-180 euro
rx 480 power draw is 150W, 150 x 6 = 900W + mb +cpu power, so 1000W is at the limit. 1600W i can get at 165 EUR. Less noise from psu
i had the same thing 6 x 150w plus cpu ram mobo and 3 fan and it was holding strong with a rm1000i, which can sustain up to 1050/1100 watt actually
you will be fine trust me