I took the specs for the slots from Newegg but this "3 x PCIe X16 Gen3 (16, 0, 0), (8, 8, 0), (8, 4, 4)" is from here http://www.msi.com/product/mb/Z87-MPOWER-MAX.html
Newegg is wrong! All three slots share 16 lanes so getting X8, X4, X4 is max what you can do. There is though only 1%...