from your motherboard link
dual at x8 (PCIE2) / x8 (PCIE4);
as soon as you install a 2nd graphics card slot 2 will drop back to x8
So yes with both cards you will run x8 x8
its reccomended for your mobo to use Slot 2 & 4 for this setup.
i believe this is the 2 BLACK slots on your board