get an r9 290 after the non reference coolers come out. make sure to get him a good psu so he can even crossfire it later. mantle should give a good boost to him when it comes out. Also they now come with battlefield 4 so its a win win.
never upgrade a computer for one game. it's not worth it, especially because of the recent issues with bf4 crashes and things, EA are a greedy company and you shouldn't be splashing cash so you can play a single game.