GTX 480 : 2 VS 3?

[cheeweezz777]

I currently have 2 GTX 480s I am using with O.R. with good success. (I am seeing 60-90% GPU utilization on both GPUs while rendering)

My question is- I am aware of the bottlenecks associated with 3 way SLI and general gaming apps... Is it worth it to add a 3rd GPU at this stage? I have the PSU/mobo/etc support it (and cooling- I am actually about to water cool the whole rig, as my office sounds like a small helicopter is running at the moment). Is there some sort of "fall-off"/bottleneck/limit to the performance gain of a 3rd GPU in regards to Octane? I am very impressed to see the 2 being used so efficiently, and very curious if a 3rd will yield a similar gain.

If it matters, I currently have 2 of the EVGA SC 480s. I am using Octane with the C4D plugin , and exporting animations...

I also wonder if it would behoove me to instead wait for the 3GB cards to arrive and upgrade there instead of a third 480...(vram vs. speed, I guess??)