OCC has published a new review of the ASUS P5K Premium Motherboard

This board features two 16x PCI-E slots one blue for 16x operation and the other (black) that runs at 4x and can run any card from 1x to 16x with a maximum speed of two GB/s. These two ports are crossfire compatible. Three standard PCI slots and two PCI-E 1x slots are also available. If dual graphics cards are used with the stock or aftermarket heatsinks accessing the PCI slots may prove difficult. Using water cooling would be a way to eliminate that as a concern. Many of the connectivity options are scattered along the bottom and right hand side of the board. These include the front panel USB and Firewire as well as the front panel high definition audio, an additional com port and the high definition audio header.

ASUS P5K Premium Motherboard Review