It appears MS is running a stacked die. Starting to see that with guys like Xilinx in the FPGA world, who also use TSMC as their fab. It's possible that the APU has some more tricks up it's sleeve. At the very least, there appear to be a lot of hard cores (co-processors, etc.) that offload workload from the CPU/GPU.
At the end of the day, it would appear that both consoles will push great visuals. Going to come down to the games (shocker).