I have been having some weird issues with SLI @ 4K lately (possibly longer without being aware 
)
Basically I am seeing strange frame rate capping but also reduced performance at frames below and close to the limit(77ish). In CSGO for example I have just left it on single GPU as it is not that demanding. In GTA it was annoying me so I have been trying to figure it for several days now. Can reproduce it by loading up 4K 60Hz in Dragon Age, 3D Mark (uses desktop resolution settings upscaled), Heaven, CSGO etc and setting on low. Will cap on 77fps if SLI is enabled. Can then even tab out - change refresh to 30 and back in to find FPS shoot up to expected levels.
Finally figured out that it performs fine if set to 4K @ 30Hz so have been testing custom resolutions/refresh rates today and can get to about 45Hz fine then bam anything above the issues above. 45Hz = 397MHz pixel clock so upon some googling seems there are some limitations around 400MHz in SLI.
Do you think that my SLI bridge is the problem? I have 3 and all show the same issues but they are at least 3 years old each
Firestrike comparison when desktop set to 30Hz vs 60Hz
http://www.3dmark.com/compare/fs/4680884/fs/4711753
And even Ice Storm Extreme
http://www.3dmark.com/compare/is/2913531/is/2912623
)Basically I am seeing strange frame rate capping but also reduced performance at frames below and close to the limit(77ish). In CSGO for example I have just left it on single GPU as it is not that demanding. In GTA it was annoying me so I have been trying to figure it for several days now. Can reproduce it by loading up 4K 60Hz in Dragon Age, 3D Mark (uses desktop resolution settings upscaled), Heaven, CSGO etc and setting on low. Will cap on 77fps if SLI is enabled. Can then even tab out - change refresh to 30 and back in to find FPS shoot up to expected levels.
Finally figured out that it performs fine if set to 4K @ 30Hz so have been testing custom resolutions/refresh rates today and can get to about 45Hz fine then bam anything above the issues above. 45Hz = 397MHz pixel clock so upon some googling seems there are some limitations around 400MHz in SLI.
Do you think that my SLI bridge is the problem? I have 3 and all show the same issues but they are at least 3 years old each
Firestrike comparison when desktop set to 30Hz vs 60Hz
http://www.3dmark.com/compare/fs/4680884/fs/4711753
And even Ice Storm Extreme
http://www.3dmark.com/compare/is/2913531/is/2912623