Well i can defenetly say ive got a good CPU and memorey,
[email protected] and 6 gig corsair dominator, maybe its something with the 5 series specificaly then, but theres about 6 of us on ati cards at the moment going to rift and none of us are on ultra as it flops below 30 far to often to be playable, id still go nvidia if playin rift though, if i can smash the fps i get from a 460 over my 5970 at 1000/1400 to me the choice would be to stick with nvidia, though if what you say is true then maybe the 6 series is worth a shot, but as OP wants to use nvidia id still reccomend a 580 with his £400.