SLI PCI-E lanes bandwidth

[mldvn33]

I have the Asus x99-A II motherboard

Intel 6850K with 40 PCI lanes

Nvidia GTX 1080 SLI with HB bridge 

Intel 750 PCI-E SSD

 

Per manual instructions I installed GPU 1 in PCIEX_1 slot, GPU 2 in PCIEX_3 slot and the SSD in PCIEX_4 slot,

then I noticed GPU 1 was only running at x8 lanes! Later found out that PCIEX_1 & PCIEX_4 share bandwidth! 

 

I'm not sure any other configurations are possible since PCIEX_2 slot sandwiched between the GPUs is only Gen 2.0 and that shares bandwidth with a whole bunch of other features.

 

I've read everywhere that x8 vs x16 is utterly insignificant but I've also read that it is more significant with modern games and especially modern GPUs like the GTX 1080. I'm even more concerned since it's the PRIMARY GPU running x8 and not the secondary, and many games don't even use the secondary GPU which would just be sitting there with all of its x16 lanes! 

 

Any suggestions? 

 

[NumLock21]

It should run at x16 in both gpus. Look at manual for proper slot configuration.

[iRileyx]

You won't even notice a performance difference from it running at x8 instead of x16.

 

Have you searched around the bios/looked at the manual to see if there's a way to change what they run at?

[knightslugger]

I have read similar things. Everyone that runs a 6700k or 7700k runs at 8x in SLI, and they seem quite content.

[Dabasepc]

1-3 FPS difference isnt something to worry about. but that should be 16x...

[mldvn33]

Yes guys as I stated I did look at the manual and bios, and as I wrote in the original message it's running slot 1 at x8 because it's sharing the bandwidth with slot 4 which is used up by the SSD, I just wanted to see if anyone has any real world evidence that a GTX 1080 still isn't very different with 8 lanes vs 16 lanes especially with modern games, that's all. Thank anyway.

[mldvn33]

On 3/17/2017 at 4:23 PM, Dabasepc said:

1-3 FPS difference isnt something to worry about. but that should be 16x...

 

On 3/17/2017 at 4:22 PM, knightslugger said:

I have read similar things. Everyone that runs a 6700k or 7700k runs at 8x in SLI, and they seem quite content.

 

On 3/17/2017 at 4:21 PM, RKRiley said:

You won't even notice a performance difference from it running at x8 instead of x16.

 

Have you searched around the bios/looked at the manual to see if there's a way to change what they run at?

 

I did my own real world test,
Switched from x8/x16 to x16/x16 by moving my NVMe SSD to the PCIE 2.0 x4 slot
Running on an ASUS 3440x1440 G-SYNC monitor
MSI Seahawk X GTX 1080 x2 (SLI)

Ran Wildlands: Ghost Recon at "very high" preset
x8/x16 SLI I got 76 FPS
x16/x16 SLI I got 95 FPS

I was surprised to find this difference but I double checked that the environment was identical and this is the result