Is gtx 260 896 mb Overkill ?

Hello everyone.My question -

is gtx 260 896mb overkill for a physx card.
i am getting a gigabyte gtx 260 896mb card for just $100!!!!!!!!!!!!!!!!!!!!!!
whats your suggestion?should i go for it or now.
by the way i have a msi lightning extreme gtx 580 3 gb card which is a monster.
it cracks every game that i throw.i game on a 27 inch asus monitor.but in metro 2033
i get 40~50 fps(average)with every settings at there any problem?or the game needs more power?
will a dedicated physx card will make any improvements?

My specs-

thermaltake armour plus full tower
2600k@4 ghz.
Asus maximus extreme
8 gb corsair dominator
2X WD black in raid 0
Crucial 128 gb ssd
CM silent pro 1000w PSU
(i think that much info is enough)

SO please help!!!!!!!!!!!!!!!!!!!!!!!!!!!! :fou: :D