w318ti
If this board is pcie 3.0 you really shouldn't see a performance difference between the x16 or x8 slots, so you should have a lot of options.

With pcie 2.0 yes you may have a small performance decrease using the x8 slots vs the x16 slots, so best to stick to the confirmed x16 slots if possible.
 
 

It is three point zero...
 

SilentMarket
You didn't force me :), I decided it this way. 
I've started a new thread on motherboard forum.
The owner RMA the board because of the sound card problem and received a new board with a new serial number (with a 3-year warranty left, 937 days exactly) and he doesn't test it when returned back.
The board hasn't been delivered yet, so I really don't know its condition and need to test it myself with old 980s when it arrives.
 

 
Good. ^^ I will move to your other thread. + If you wanna see your new board, you can go to my "Mods Rigs".
 
Edit:...

CriticalHit_NL
You really wanted those 100 posts didn't you? :P by judging your post history. (I saw your smileys pass through random threads and I wondered why)

It is odd that some of our new Elite Members Frist Action here on the Forum is to get Banned
Their Post Count should be reset to -100 and then give them a second chance IMHO.

bcavnaugh

CriticalHit_NL
You really wanted those 100 posts didn't you? :P by judging your post history. (I saw your smileys pass through random threads and I wondered why)

It is odd that some of our new Elite Members Frist Action here on the Forum is to get Banned
Their Post Count should be reset to -100 and then give them a second chance IMHO.

 
Even if posts are removed the post count does not decrease, currently
 
They get PM warnings about such posts, if they persist on meaningless post ...... they get a temp ban

Update: gear upgraded from Z97 to Z270 because the performance is limited with 4790K, SLI scaling is not good. PC can't do 4k in Rainbow Six Siege. And PLX switch decreases performance somehow in Z97 Classified.
So I upgrade the motherboard to ASRock Z270 SuperCarrier. The board has 2 slots spacing with double x16 enabled by PLX switch. Temps are even lower because of the lower fans, max 64C in GTA V and Ghost Recon.


 

It does have a big difference in 4K. After I changed the motherboard to Z270 with 7700K, the SLI scale can reach 99% in Rainbow Six Siege. But with 4790K the SLI scale can only be around 50%. 

Carbonshape
Okay, but I don't get it. The Z97 has a PLX PEX chip that will work with 16x16x etc. + The web is full of examples. But as I said, main thing your good with your new platform.

because I didn't use 2 and 4 slot for SLI, too close, too much heat.

Come back five years later.
Generations of CPU bottleneck 4790K vs 7700K vs 8700K vs 9900K and above was something rare non-SLI users would've ever encountered back in 2017. It doesn't even matter much using x8/x8 or x16/x16. 
Without the similar rig, whatever the troll Stardust_One were talking about was off the rail.