Should two GTX-1070s be "strapped" together??? [FAH: Y or N]

[bruce]

As I understand it, SLI/XF enables two GPUs to share the video rendering by generating alternate images and merging them into a single video stream. This is useful if you want a higher frame-rate in your game.

FAH does not produce rendered video so it doesn't use the video rendering components in your GPU, nor does it care how or where that occurs. FAH does use the 3D compute components ("shaders") of each individual GPU, independently from those in any other GPU, including one that happens to be strapped.

In order to render your game's frames twice as fast, the 3D computations needed for both half of the game's images will generally consume a bigger percentage of those shaders resources, so the total amount of work completed for FAH will, in fact, be less. as the FAHCores will do more waiting on the game. This naturally will reduce the total PPD. I'm not aware of any other specific cause for FAH performance to be reduced except for a different level of contention for whatever competition that it sees for resources needed by both the game and by FAH. -- including things like the PCIe bus, VRAM, etc.

The same is true when your OS happens to use the GPU to update your screen, but that's much less significant that running both a game and FAH concurrently.