On the underside, we see that the C5F-Z has ditched legacy PCI of its predecessor in favour of a PCIe x1 slot. The board supports up to 3-way SLI/CrossfireX which entails that it won't be participating in any 4-way action. Like on their recent Intel boards, ASUS has also implemented T-Topology on the DRAM traces to improve clock mileage when all DDR3 DIMM slots are populated.
Large heatsinks tightly secured by screws are placed over the 990FX Northbridge and MOSFETs, which can get uncomfortably toasty during overclocking. You will definitely need active airflow in that area to keep switching efficiencies high and prevent any clock throttling.
The same 8+2 phase digital dual driver design is carried over from the previous board, although the PWM controller has been replaced with a newer model. ON Semiconductor NTMFS4955N/4937N Power MOSFETs used here are some of the best in class.
Over at the edge of the board, we see that the power and reset buttons have been re-deployed to an optimal spot next to a PORT-80 debug LED (godsend for debugging) and LN2 slow mode toggle (forces lowest CPU multiplier). The memory VRMs have also been upgraded to a digital solution to give faster transient reponse in an effort to squeeze out more megahertz.