iPhone 5CS? I wonder if they'll position the 5C as the low-end in developed markets, the "5CS" where the 5C is now, and the "6" as the new high end? Sales of the 5C haven't been radically different from previous "old model" iPhones, and FoxConn has gotten really efficient at making the aluminum cases, so it's still conceivable that they will keep the 5S around as the mid-range.
We haven't seen any leaks from the purported 5.5" model, but we haven't seen any "5CS" leaks, either (though that would be easier to keep a secret since it just involves putting the 5S innards into the 5C case).