Network card in PCI E x 16 slot

I have the Killer Nic M1 network card:

http://www.bigfootnetworks.com/killer-nic-m1/

The problem is that I have run out of PCI e x 1 slots and only a PCI e x16 slot free on my Asus Extreme Rampage mobo.

my quiestion is can I use the PCI e x16 slot for this network card?

Thanks

It is supposed to work in theory but it depends on how sloppy the mobo manufactor complies with PCIe specs.

8-bit ISA could be used in 16-bit ISA slot, and either version of ISA card could be used in EISA and VESA slot without a problem.

Yep: Google search lead me to Tom's Hardware forum with this question and many answers:
http://www.tomshardware.com/forum/205984-33-card-slot