If the 660 gtx SC is a non ti, get the 660 ti, it's better, more cuda cores, texture units, overall it's better and if it's really a non ti the SC, it's really overpriced.
So get the 660 ti on ebuyer.
If the SC is indeed a 660 ti, then get the SC on amazon, it has a higher overclock from factory, but make sure it's the ti version.