FCPX: are 3 GPUs better than 2

[pjjj]

In this message, Rob mentioned "dual 280X cards work very well, triple even better".

Can Final Cut Pro X really use a 3rd GPU?

I spent quite a bit of time searching and reading many threads. Found LOTS of benchmarks showing 2 GPUs matter, that AMD is much better supported than nVidia, but I failed to find anywhere that anyone has confirmed running 3 GPUs at all (of any type), not to mention whether it helped with FCPX, like BruceX benchmark time, interactive performance, far far away render test, etc.

I've got two R9 280X on order now. At 3rd new one would add another $250. Is there anyone who's ever tested a 3rd GPU? Would a 3rd card be beneficial, or "diminishing returns", or have no effect at all, other than eating up another $250?

 

[pjjj]

I'm getting the feeling nobody in the entire world has ever actually tried 3 GPUs with FCPX. Well, outside of Apple employees with strict non-disclosure agreements....

Guess that's not too surprising, since 3 GPUs can't really fit into older mac pro towers, and others macs can't be upgraded at all. Most hackintosh builds probably never use more than 2 either, if not for lack of physical space, probably for lack of funding.