Multiple Monitors and Multiple Graphics Cards

[Geldar]

Something interesting happens that i cannot explain, im probably not understanding properly how multiple GPU's operate.

 

I have a r9 290x which i use to drive my 3 1080p monitors. I only ever game on the primary centre one, the 2 secondary monitors are for watching movies, web browing etc (all low intensity stuff).

 

I had an idea that if i use an older (but still more than powerful enough) 6870 to drive my secondariness and dedicate my primary monitor to play games i could squeeze a few more FPS out of my games.

 

The actual results are different than i thought, it actually runs at 2-4 FPS less with 2 GPU's than a single GPU. I cannot explain why as the 290x is driving less pixels than it was before!

 

Both cards are running in 8x mode which i understand is usually not a limiting factor. 

 

Can someone explain to my why this is the case?

[Jaybird]

probably more processing allocated to telling the gpu to do stuff. like if your boss has to tell two people to do two different jobs in stead of one person, one job.