Which GPU to choose?

Im thinking of upgrading my gpu, currently has the Sapphire hd7950. I upgraded my pc with a AMD-midrange pack 6 months ago, a gpu wasnt included. I wonder how much the difference is between RX 470 8GB and RX 480 4GB. And which of the cards you would recommend getting? They are priced exactly the same. (Im going to upgrade to 16gb ram at same time).

I mainly play games but also tinker in blender and plan to learn Unreal engine 3.

 

Current hardware is:

CPU: AMD FX-8350 Black Edition @ 4.0 Ghz

RAM: HyperX Fury 2x4GB DDR3 1600 MHz/s

GPU: Sapphire Radeon HD 7950 3Gb GDDR5

Mobo: Asus M5A97 R2.0,socket AM3+

HDD: HyperX Fury SSD 120GB

Secondary HDD: Seagate SSHD 2TB

PSU: Silver Power SP-SS500 500W