Right here: "Computer Interface PCI Express 4 lane, compatible with 4, 8 and 16 lane PCIe slots."
The sabertooth has the following:
* PCI Express 2.0 x16 (2)
* PCI Express x16 (1)
* PCI Express x1 (1)
* PCI Slots (1)
So you can stick it in the regular x16 slot.