I'm not in the loop of current events, but many guys here have RX460 so they'll answer you soon enough.
My assumption is that all is ok.
Non flashed AMD cards are working at PCI-e 1.1 speeds in cMP, and RX460 is a x8 card. So speeds you're getting are expected when using just eight lanes of first gen PCI-e interface.
Hope that someone will correct me if I'm wrong.
EDIT: Haha, one minute faster 😀