4870x2 problems

hi i bought my first grafix card as an up date i got an hd 4870x2
i thought this was a great card but it dosent seen to be that great
i can run
cod 4 maxed
cod waw maxed

cod mw2 maxed but low ish fps when loking into middle of map
but when i try to play mw3 that i just bought for £35   it gives a low fps soo i put everything on low i still get a low fps
and skyrim on medium is an ok fps but not great

i was wondering if its my pc or if its the grafix card isnt as good as i thought
my specs are
4gb ddr2 ram
phenom x4 9550
hd 4870x2
windows 7 ultimate x64

soo if the grafix card isnt that good i can sell it and buy a diffrent 1 for about £70-£80 $110-$127 i can go a little over or under just the best for around that price
soo if you know the best 1 in that price range recommend it or if you know what is wrong plzz help and thx if you need anymore info msg me or if you can help plz post