Motherboard PCIe modes question

I have a question about PCIe modes. I want to SLI two huge two and half slot cards so I want to buy a 4-way SLI motherboard and use slots 1 and 4 to give the cards maximum separation.
I plan on using an i7-5930K to get the 40 lanes. Now here are the specs on the ASUS RAMPAGE V EXTREME/U3.1 LGA 2011-v3 Intel X99

PCI Express 3.0 x16: 4 x PCIe 3.0/2.0 x16 (x16, x16/x16, x16/x8/x8 or x16/x8/x8/x8 mode with 40-LANE CPU; x16, x16/x8, x8/x8/x8 mode with 28-LANE CPU) *2 *2 The PCIE_X8_4 slot shares bandwidth with M.2 x 4. 40-LANE CPU: The PCIeX8_4 slot can only be used in x4 mode or lower when used simultaneously with the M.2 connector. If x8 mode is used, the two connectors will be mutually exclusive. 28-LANE CPU: The PCIE_X8_4 slot will be disabled and the M.2 connector will always be enabled.

Obviously if I use the first two slots I will get x16/x16, but will that be true if I use slots 1 and 4?

Honestly, it won't matter, there will be enough bandwidth to cover the card even if the slot does go x8. This has been shown in quite a few different tests.

Here is a really good one https://www.pugetsystems.com/labs/articles/Impact-of-PCI-E-Speed-on-Gaming-Performance-518/