I don't think its the ram at all 8g is more then enough for bf4 but if your cpu is 100% that should be a dead give a way games hardly use more then 65% for the cpu most of the time bf4 is normally at 45% with me and I'm using a amd fx8350
I think the rx480 if you want to future poof you pc for year or 2 but if you don't care about that the gtx1060 might run some dx11 gamers better im not 100% sure but rx480 well be better for newer gamers that will run on dx12