Posted 20 March 2013 - 19:39
I have the same rig, and while my gfx cards are quite old now, they still pack a punch to run any games I want at 1080 without a problem.
There is still plenty of life left in that rig yet.
Cheap options, you might want to overclock the CPU The 920 is a nice CPU and a lot of the time you can get 3.2ghz without a problem on air, depending on your cooler of course.
xfire with a 2nd 4870 card off ebay on the cheap. You'll be able to pick them up for peanuts now and while you won't get an amazing bump in speed you should notice it for the price...but
Your GPU is the bottle neck in the rig at the moment. You should consider upgrading that to something nice and beefy before spending the cash on other parts that won't give as big as a performance boost.