Impact of fewer PCIe lanes on GPU

[Clolarion]

My rig + GTX 1070 AMP! Edition

Right now my 1080 Ti is in the PCIEX16 slot and the 1070 is in the PCIEX4_1 slot. When gaming my monitor is plugged into the 1080 Ti so I gave it the slot with more PCIe lanes. The 1070 is still in my rig for mining and the 1080 Ti mines when I'm not using it either. According to my motherboard's manual and GPU-Z the 1080 Ti should and does run at x16 and the 1070 at x4 with the 960 EVO running at x4 as well. However I've found that when I'm mining with both cards they reach temperatures as high as 91C because that's a lot of heat from 2 overclocked cards and the 1080 Ti is fat (3 slots thick) so it sits directly on top of the 1070 (in fact it weight and length causes the end of it to rest on the 1070). I'm considering swapping the 2 GPUs to increase airflow but that would mean the 1080 Ti would be running on only 4 PCIe lanes as opposed to 16. What kind of performance loss would I see while gaming if it were to be running at x4? Also, I've heard that the 1080 Ti has a thermal throttle that kicks in at 84C, would that outweigh the loss in PCIe lanes?

 

[Kasper Jorgensen]

You will take a great performance hit for sure by doing that. What you may want to consider is getting a motherboard designed for 3 or 4 GPUs and you can then place the GTX 1080 TI at the top and the GTX 1070 at the bottom, leaving more space between them.

 

[DRagor]

Just swap the cards and see for yourself exact answer to your question, instead of ours educated guess. 15 min of work and you will know what kind of performance hit you'll get.
However I doubt swapping cards will help much with temps. After all, amount of heat your system generates will not change, only distribution of air. It will certainly help 1080ti, but at a cost of worsening 1070 temps.