Nvidia cards selection

[Bowme]

Long story short i had a GTS 450 from Nvidia, which frankly died. The company i brought the computer from then replaced the card with a ATI radeon hd 5700 claming that its was about 5% better than my current. i am not a big fan of ATI and surely the card could not handle my 3 wow windows im goning with... and ive just decided to jump up to a 5 man team

So here I stand, im about to call the company tomorrow and Ive checked their homepage to see the replacements they could offer me( Im using them again, cos they're willing to give me a small cut of the price). My goal with the new card is to have 5 wow windows runing with atleast -2030ftps on 4 of them and 50-60 fps on the main window. Ofc I could just go for the expensive one, but i think that would be an extream overkill compaired to the rest of the pc

some info about my pc
2 monitors both DVDI
SSD
750 psw
i7
8gb DDR3

Their Nvidia cards

Nvidia GF GT 520 1GB DDR3
(53,56 Euro)

Nvidia GF GTX 550Ti 1GB DDR5
(140,82 Euro)

Nvidia GF GTX 560 1GB DDR5
(173,03 Euro)

Nvidia GF GTX 560Ti 1GB DDR5
(187,8 Euro)

Nvidia GF GTX 570 1280MB DDR5 (Nyhed)
(281,9 euro)