Intel HD Graphics and CPU performance
I have 3 monitors connected to my PC. 2 of them are connect to my crossfired HD7870 while the third is connected to intels APU/Intel HD integrated graphics. I was wondering if it would be more efficient (power-wise and/or performance-wise) to plug the third screen to my HD7870? The reason I have used the integrated graphics is due to the having 2 VGA only screens, and the HD7870 only supports 1 analogue screen. It was obviously cheaper not having to buy an adapter. But I was wondering what effects the two options have, and what is preferable and why.
I would say power consumption wise, it would be more power efficient to connect the 3rd monitor to the Intel HD graphics core. Since the CPU is designed using the smaller 22nm die process as opposed to 32nm (I think) for the Radeon HD 7870, power consumption should be lower.
From a performance stand point, it is also better to simply use the Intel HD graphics core for the 3rd monitor as well. Even when playing games on a single monitor, as long as the 2nd monitor is connected (even if the monitor is off), the Radeon HD 7870 still need to refresh whatever is being displayed on the 2nd screen such as an empty desktop. Connecting the 3rd monitor will decrease performance further since the Radeon must also refresh the desktop on that monitor as well.
The overall impact on performance is probably 2% or 3% per monitor if nothing is being displayed except for the desktop.
It really doesn't matter unless you want to eyefinity then you need all the monitors on the 7870. Power is negligible, depending on which hd graphics you have it's only 20-30w max, gpuz is saying my hd 3000 idles at .4w, any gpu tasks still run off my discrete so I never see it go above 1w. So this equates to less than a dollar per year. Using the igpu is higher power consumption, not sure why you said it would be lower. You got 2 gpus idling instead of 1.
Where did you pull 2-3%?