Does card placement for SLI/Crossfire setups matter.

[ProtoAMP]

I'm planning to get 2x reference cards from Nvidia and was wondering how much the placement mattered. I understand that placing one directly above the other will cause the top one to be much hotter and subsequently have lower boost, but would it throttle and if so would it be a big enough dip in performance?

Info:
CPU is cooled via liquid
MSI x99s Gaming 7 motherboard
Phanteks Enthoo Luxe Full Tower Case
Picture for reference is my 980 ti AIB, which will be replaced with 2x founders cards.
https://imgur.com/a/Q9MJS

The one on the left looks cleaner IMO, but doesn't give the card in slot 1 much space. Any help is massively appreciated. Thanks!

 

[little_me]

yes and no.
from https://www.msi.com/Motherboard/X99S-GAMING-7.html#hero-specification
Slots

• 4 x PCIe 3.0 x16 slots, support up to 3-way mode
- 1-way mode: x16/ x0/ x0/ x0
- 2-way mode: x16/ x16/ x0/ x0*, 16/ x8/ x0/ x0**
- 3-way mode: x16/ x16/ x0/ x8*, x8/ x8/ x8/ x0**

• 2 x PCIe 2.0 x1 slots

* For the CPU that supports 40 PCIe lanes
** For the CPU that supports 28 PCIe lanes

So if you want both cards to be at 16x bus speed, you must use first two slots (and have nothing in other 16x slots.)
Of course if your CPU wont support 40 PCI-E lanes but 28, it's non issue since other will drop to 8x anyway.

Edit: According to that, you either use top two and if you go 3 way, top three or top 2 + bottom.
It could work or it could not work in other configurations.

Edit2: Since you have wifi card and GPU's block both 1x speed slots, you would have to go with top2 +wifi in 3rd 16x slot, ending with GPU's running on 8x bus speed.

 

[ProtoAMP]

yes and no.
from https://www.msi.com/Motherboard/X99S-GAMING-7.html#hero-specification
Slots

• 4 x PCIe 3.0 x16 slots, support up to 3-way mode
- 1-way mode: x16/ x0/ x0/ x0
- 2-way mode: x16/ x16/ x0/ x0*, 16/ x8/ x0/ x0**
- 3-way mode: x16/ x16/ x0/ x8*, x8/ x8/ x8/ x0**

• 2 x PCIe 2.0 x1 slots

* For the CPU that supports 40 PCIe lanes
** For the CPU that supports 28 PCIe lanes

So if you want both cards to be at 16x bus speed, you must use first two slots (and have nothing in other 16x slots.)
Of course if your CPU wont support 40 PCI-E lanes but 28, it's non issue since other will drop to 8x anyway.

Edit: According to that, you either use top two and if you go 3 way, top three or top 2 + bottom.
It could work or it could not work in other configurations.

Edit2: Since you have wifi card and GPU's block both 1x speed slots, you would have to go with top2 +wifi in 3rd 16x slot, ending with GPU's running on 8x bus speed.

Oh right, that makes a lot of sense. Thank you! Do you think something like the 1080 ti would saturate an entire x8 lane (I'm using the 5820k with 28 lanes)? Thanks.

 

[little_me]

according to this:
https://linustechtips.com/main/topic/608355-gtx-1080-pcie-30-x8-bottleneck/

No difference at all.

 

[ProtoAMP]

according to this:
https://linustechtips.com/main/topic/608355-gtx-1080-pcie-30-x8-bottleneck/

No difference at all.

Brilliant. Thanks a ton!