Grab a 7870, it will provide a substantial boost in performance. Battlefield 4 is optimised for AMD, so it would be the better purchase by far. You could grab a 7950 for a tiny bit more than the 7870. What's your budget?
The 7870 is in the recommended card from AMD, so you should be good to go with that. The 7950 is a BEAST, especially if you grab a variant that OC's well!
The cheapest 7950 is about 100 Euros more expencive than the 7870 so thats not really an option, my budget is about 150 + the money i get from selling my Gtx 650. I found an Gigabyte GTX 660 oc for 180 Euros that includes Batman, witch i was going to buy anyways, so that would be pretty cheap. But how well will it handle games compared to a 7870?
That PSU is a definite overkill. I have a 7990 coming in, in a couple of days with an 850w psu and that is relatively enough for it. For battlefield. In most cases the AMD gpus are your best bang for you're buck and they overclock amazingly well.
yeah, i know the powersupply is overkill, but i traded it with my dad, i gave my corsair cx 430m. Thats sounds like i plan, i'll wait and then decide, two weeks isnt that loong.