FCPX performance with a single display vs dual displays?

Is there a performance advantage to using a single display instead of dual displays?
Especially for *rendering* a clip with effects in the timeline (as opposed encoding h.264 or exporting to a master file, which I'm happy to leave running overnight if need be).

I can't seem to find any definitive results on this... largely because any Google search with the words "final cut" and "performance" inevitably returns a billion hits on selecting "performance" vs "best quality" for play back in the Viewer. Searching on "speed" instead of "performance" returns a billion results on adjusting clip speed. Ugh.


If there is a performance boost to using a single display, how much of an improvement is it?

I believe there is a performance boost with one display running as opposed to 2 or 3, but the extent of that boost will depend on your system and specific graphics card. It should be an easy test to disconnect one display and use FCPX with and without it connected to see how it might help. For reference, we are using a MacPro mid 2010 12 core 64 GB ram with ATI Radeon HD 5870. The GPU drives 3 displays (2 Apple 27" LED displays via mini display port and 1 Samsung 19" LCD display via DVI). We also have a 4th display (LG 42" HDMI) connected to a BMD Declink PCIe card in the Mac Pro for FCPX AV output. It seems by turning off AV output, the system is a bit more responsive but hard to tell. We usually use all 4 displays running and things seem to function pretty well.

Hi Erik
There is both a short answer and a long answer to this question.
Short answer. Yes, using 2 or more monitors can cause longer "effects rendering".
Long answer, there is no definitive single answer as to how much will this affect speed. It depends on way too many factors.
Having more than 1 monitor uses more computer resources, RAM, CPU, GPU, bandwidth, and an environmental energy factor. You can spy on this via Activity Monitor.
What computer you have, what processor, type of monitors and resolution of them, lots of different things can change how much, a little or a lot in rendering speeds.
If you have a top of the line computer with a great GPU, lots of ram, you may not even notice any slowdowns. If you have a lower end configuration, high resolution monitors, doing 4k multi-cam video, might be slower than molasses in January. Stutters, dropped frames, etc…

dgvideo's comments/suggestion is a valid way to test.

I use 2 or more monitors while editing, but consolidate to 1 normally while exporting but mainly for other reasons than speed.
I find the use of 2 or more monitors while editing worth any small penalty in speed while editing. In general I move all of FCPX to an external monitor, then show viewers on my rMBP so I can see only the clips and scopes on the retina while my browser and timeline are on a larger but less accurate color monitor.
Hope this helps, Greg

Thank you Dgw and Vid.

I think I'll run a few tests. I suppose I'll even post the results here if I find anything interesting.

1 vs 2 monitors comes down to GPU only, period. Plug in a second monitor and applications that can utilize the GPU only have half that GPU's resources automatically. That's an OS X thing. More powerful the GPU, and more VRAM it has, the less you'll notice any performance degradation.

Thank you everyone