GPU render with multiple cards: Does card order matter? I recently added a new card to my system. I am running a Titan X and 770. When testing my render speed, I found that, for the same scene and same samples, the 770 took 1:53 to render it, and the Titan took 1:20. However, with both working together, it took 1:16...only a 4 second improvement over the Titan alone.

I know that you don't get the full power of the second card, but this seems a little extreme. In Blender's options where I select the compute device, it lists 770+Titan, with the 770 first (The titan is in the primary motherboard slot and runs 1 of the 3 displays.) Does this mean it's primarying the 770 and then not making full use of the Titan? How do I fix this?

EDIT: When watching my GPU monitor, I can see the 770 being used, but the Titan rarely shows activity above a couple %. It seems like the 770 is getting all the tiles or something. What's with that?

EDIT 2: When testing viewport rendering, things actually slow down when using both cards vs using just the Titan.
So I just tested this:

No, card order does not make a difference. Doesn't really matter which one is set as system (if the system is doing nothing) or to which the monitors are plugged. The render times were off by fractions of a second (BMW benchmark scene with 2 cars).

Both my cards are in PCI Express 3.0 at x16 slots.