Save some money and upgrade pal. You kit is from the arc and you are trying to play modern games on it. If you staying on the tight ass skinflint route, buy 2nd hand from here.
Just save at get 960. Just cause 3 is 40 quid, could hold off on that for a month and use that towards gfx card. 960s going for 160 odd quid.
If you're set on a 960 there's a Gigabyte model going for £145 on Amazon atm, pretty good deal. Also an Asus if you prefer a blower style fan on OCUK for £150- though the 960 isn't exactly going to throw out a lot of heat anyway.
http://techbuyersguru.com/video-card-comparison-blower-style-vs-open-air-coolers Mildly interesting article that explains it better than I would.