your 580 does not struggle with PS2, without going into too much details PS2 is in beta and they have not released all the "settings" to max out that game, once it has been fine tuned then your 580 will max it out easy.
TBH anything over 60 FPS is wasted on the human eye i certainly cant see any difference in it
the 690 i a waste of money buy 2 x 670 if you wanna waste money, 1 x 670 is enough to max all these games out,