Rampage V PCIe speeds


Can`t understand one thing about PCIe speeds. In Asus Rampage V specs mantioned that it has 4 PCIe x16 slots:

"4 x PCIe 3.0/2.0 x16 (x16, x16/x16, x16/x8/x8 or x16/x8/x8/x8 mode with 40-LANE CPU...)"

What does this mean 16/x16, x16/x8/x8? Does it has difference between x8/x8 or just x16? Or this is a SLI thing, i really confused. I see that on the motherboard itself marked only 1st and 4th slots with label x16.

I asking, because installed on it Noctua NH-U14S and 1st slot is obstructed now.

What slot should i use for my videocard for best performance?

other specs:
intel 5930K
asus 980 Strix

16x, 16x/16x etc. is indication of the PCIe slot speeds with that number of graphic cards. Second red slot should be fine to plug your card into.

Thank you, i`ll do it.

Ok, but i can`t understand, why in the manual 2nd slot is only x8_2 but 4th x16/x8_3? Is it have at all no difference with one videocard?

At closer inspection of the manual, page 1-19, you should probably put it in the second pxie_x16/x8_3 slot, that said, afaik few(if any, sure someone will correct me if I'm wrong) GPUs today actually utilizes the full speed of PCIe 3.0 16x, but then again, that could be in SLI configurations.

On a side note, why not get a different cpu cooler, or turn it 90 degrees?

Wanted to have a Kingston Predator DDR4 and it's got height in it and can't find descent watercooling loop in my place. Over here people selling only small 120x120 noisy stuff and no Corsair or something good, so decided to buy Noctua NH-U14S.