Agree with Embra, the 6950 should be running WoW well enough and the rest of the system is easily up to the task, if you're planning the upgrade for ESO I suggest you hold fire and wait until you see how your current rig performs before making a possibly costly mistake.
Of course if you're going to start playing graphically intense games like FC3, TR, BF4 etc then the GTX780/770 makes perfect sense and I'll suggest you go for the GTX770.