Hd 5970

i just popped a brand new 5970 into my system and when playing bf3, i get the same frames as i would with a 6870?! i was hopping you could tell me what the issue is. i got all the latest drivers, phenom x4 965 @3.4 ghz, 8 gb ddr3 1600 ram. x16 motherboard. thanks in advance.