For my universal app, Forex App, I'm simply using the screen height detection concept like so:
CGSize screenSize = [[UIScreen mainScreen] bounds].size;
if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone) {
if (screenSize.height > 480.0f) {
/*Do iPhone 5 stuff here.*/
} else {
/*Do iPhone Classic stuff here.*/
}
} else {
/*Do iPad stuff here.*/
}