The 8GB RAM, while not useful now, will be as games progress to use more VRAM. And the 390X goes toe to toe with the GTX 970 pretty well, even beating it in some situations on some games - for less money.
Honestly, I am playing GTA V on max everything at 1080p and still getting smooth frame rates. Not sure the exact FPS because I haven't had my overlay up yet as I just got the game last night, but I will check it out when I get home from work.