This picture surfaced today, showing an "A7" SoC. iOSDoc claims that this chip is a quad-core, clocked at 1.2 GHz. It is also expected to include a PowerVR quad-core SGX554MP4 GPU, with 2GB of RAM (Dual-channel LPDDR-800). The iPhone 5S is also expected to run iOS 7, with its many new features.
Source: iOSDoc