gtx680s in Surround perform differently depending on monitor connections/assignments

I have two EVGA gtx680 FTW 4GB cards in SLI that I use with 3 x 120Hz monitors in surround. The performance seems good even with my old i7-860 at 3.8GHz. I was getting this result in Heaven 3.0 until I decided to move the DVI cables.

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Heaven Benchmark v3.0 Basic
FPS: 95.4
Scores: 2404
Min FPS: 30.4
Max FPS: 235.6

Hardware
Binary: Windows 32bit Visual C++ 1600 Release Mar 7 2012
Operating system: Windows 7 (build 7601, Service Pack 1) 64bit
CPU model: Intel(R) Core(TM) i7 CPU 860 @ 2.80GHz
CPU flags: 3621MHz MMX SSE SSE2 SSE3 SSSE3 SSE41 SSE42 HTT
GPU model: NVIDIA GeForce GTX 680 9.18.13.479 4095Mb

Settings
Render: direct3d11
Mode: 1920x1080 8xAA fullscreen
Shaders: high
Textures: high
Filter: trilinear
Anisotropy: 16x
Occlusion: enabled
Refraction: enabled
Volumetric: enabled
Tessellation: extreme
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The monitor that was displaying the POST was on the right, so I swapped the DVI cables on the GPUs so that the POST would show up in the middle. Then I reconfigured "Nvidia Surround" and all seemed well. Finally, I executed the Heaven benchmark, 3d mark 11 etc. and every benchmark fell by about 10%! Heaven 3.0 was getting 21XX at 86 FPS, and 3dmark11 was getting 19000 GPU score instead of 21000. I couldn't figure out what had happend at first. GPU usage was hitting 99% most of the time. Finally, after reinstalling drivers and testing numerous times, I moved the DVI cables back to the original positions. The benchmarks went back to normal. What is going on here? Am I missing something? Should I test all the various scenarios to see if I get better performance

I have the center and left monitor on GPU 2 and the right monitor on GPU 1. Moving the center monitor to GPU 1 and putting the sides on GPU 2 is what results in the 10% performance loss.

I thought the entire "surround" frame was rendered alternately by each GPU. The only information I can find from Nvidia indicates that any of the 4 DVI ports between the cards in SLI can be used for surround. Please point me to any information specifying how the monitors assignments should be made.

Thanks for the link. +REP


However, all I learned was this information below about using the first DVI connector on the second card.

The recommend configuration is as follows:

•Connect two of the 2D Surround displays to DVI connectors one and two on the first graphics card, subsequently flagged as the Master.
•On the second graphics card, the slave, connect the third 2D Surround display to the first DVI connector.
•Connect the Accessory Display to the HDMI port or the DisplayPort on the Master graphics card.

This made no difference in my testing. No one else has seems to have noticed this, so maybe it is something with my system. I tried several different cabling scenarios and each had a different result. One case showed a 20% lower benchmark.