The correct configuration for the ASUS P5K-E WIFI-AP motherboard solts is:
2 x PCI-Express x1
3 x PCI 2.2
2 x PCI Express x16 blue and black (with one "black" supporting only x4 and x1)
This information is wrong because the BIOS doesn't properly expose slot information via SMBIOS DMI - as you can see they define all slots except PCIEX16 as PCI-X.