Single CPU on Dual board impedes performance??

I‘m planning another new desktop system build; both laptops are falling short. I’ve contacted board manufacturers and get conflicting answers. Hence I appeal to the seasoned ones here. System Build only half the board: ASUS Z9PE-D16 (Dual Proc, C602 server board); and starting with only one Xeon E5-2687W and 128GB Kingston (2x (4x16GB)) for the one CPU only. Some say that a terminator...