A quad core CPU for iOS is 100% useless. iOS only needs two cores and the reason for that is very, very simple.
iOS is a native CPU based application system unlike Android. IE on Android you have to run the OS, the Dalivik Virtual Machine and then the application. That is three pieces of software running just for one application. And because Android allows ANY app to run in background, whether it needs to or not, it has to have DVMs running for each app at all times. iOS on the other hand only has the OS and the application. Very few applications are allowed to run in background mode, Apple has to approve them, and that means that one core is needed to deal with the user and what is being displayed with only about 1/4 of the second core being needed for iOS to maintain the rest of the phones features.
So until Apple has a major shift in the iOS core design, there is no reason to add two cores that will simply be using up your battery for zero benefit in operation.