supersun

safan80
Use PE2  or PE5 for full 16x in the case you posted above. You  can also use a pci-e riser with ribbon cable to place the card somewhere else if you case has the room for it. Do a search for "cases with vertical gpu mount" to see what I am talking about, but you usually have to spend extra for hte pci-e extension ribbon cable to get it done. 

PE5 still works on 3.0x8 when I install the graphic card on it. It's strange and I can't find out where to manually 'correct' it. 
I set up vertical gpu once but dissatisfied with temp(more than 15 Centigrade higher than the normal side)

 PE5 – x16 (Gen3, x16 lanes from CPU, x8 shared with PE4)
 
That means if you put another card in PE4 PE5 will run at x8 no matter what.
 
PE2 – x16 (Gen3, x16 lanes from CPU, x8 shared with PE3)
 
That means if you put another card in PE3  PE2 will run at x8 no matter what.
 
https://images.anandtech.com/doci/12092/boardfront.jpg
 
Check the physical slot
Shows the the top most pci -e 16x slot and bottom most 16x slots  will run at 16x. So your card has to be plugged into one of them. As the rest run at 8x.
 
There doesn't appear to be any slot numbering so you need to choose the slots that say PCIE_X16X8. There are only two such slots.
 
 
upon reviewing the motherboard manual
 
You need to check the bios to make sure no slots are disabled or  not running at a lower speed.
 
If you can't find anything clear the bios reset to default making sure your overclocking profiles are backed up either by writing them down by hand before clearing the cmos or saving in an available profile slot if available. 
 
If everything checks out there... Double check the bios file you downloaded and if the board came with bios 1.25 try reflashing the bios using the correct file from the sticky at the top of this page. I recommend you learn the dos flashing method for flashing the bios. You can also find older bios files for prior versions using the search function on the forum. Be sure to check the changelog for bug that you MIGHT run into.
 
 
motherboard manual link
https://www.evga.com/supp.../files/142-SX-E297.pdf
 
4x PCI-E x16 slot 2x16, 2x8*
1x PCI-E x4 slot
1x PCI-E x1 slot
*LANES PER SLOT CAN VARY BASED OFF OF CPU, PLEASE SEE
PAGE 24 FOR LANE BREAKDOWN BASED OFF OF CPU.
 
 
PCI-E Lane Distribution (44 Lane SKX CPU’s)

U.2 1 – Gen3, x4 lanes from CPU (No Shared Lanes)

U.2 2 – Gen3, x4 lanes from CPU (No Shared Lanes)

M.2 Key-M (110mm) – x4 CPU lanes (No Shared Lanes)

M.2 Key-M (80mm) – x4 PCH lanes (No Shared Lanes) (*)

M.2 Key-E (32mm) – x1 PCH lane (No Shared Lanes)
 
This motherboard does NOT have any lane replication via PLX; all lanes are
native and derived from CPU or PCH. This also allows for improved backwards
compatibility for Gen 2 devices.