Question regarding PCIe speeds


Feb 1, 2011
ASUS Maximus IV Extreme-Z LGA 1155 Intel Z68 SATA 6Gb/s USB 3.0 Extended ATX Intel Motherboard

Obviously a popular motherboard. I'm having trouble trying to figure out how each of these PCI ports operate.

It says under the PCI specification:

PCI Express 2.0 x16: 4 (x16 or dual x8 or x8, x16, x16)
PCI Express x4: 1
PCI Express x1: 1

I am confused as to what this exactly means. Do the 2.0 ports operate at dual x16 speeds for SLI? I want to use two nVidia cards for SLI and I want to make sure I am getting dual x16.