We are seeing some issues with render targets while running on multiple displays on Nvidia Surround and AMD Eyefinity. From the image you can see all of the render targets for the scene capture and post process are getting blown up to 5760x4096. As you can imagine this brings the GPU to a halt (3fps). I am impressed it even runs at that point.
Our current res is 5760x1080 across 3 monitors and the render to texture size is set to 1024x1024. When running windowed without using Surround or Eyefinity we are not seeing any changes to render target sizes and minimal hits to the GPU. We are not doing anything special other than capturing the render target and displaying it within a widget.
Alternatively if there was a way to run across 3 screens without using Surround or Eyefinity that would be ideal but we have not been able to get that to work without it being compressed to the main monitor.