SLI is not needed for Octane,
You can install hardware bridge for sli ( ie for gaming!!!)
And then you can turn on and off sli easily in the configure settings when needing to.
Some say sli on slows down Octane, but I tested on and off and the difference was almost none.
It might differ with different GPU config? I do not know, because I only tested my triple 780Ti with sli on/off.
Anyway.. Go for hardware bridge and sli... It would be a shame not having triple X on sli
Ps
Triple X: wow.. Very nice way to go!
Added ps2:
In faq about sli:
https://home.otoy.com/render/octane-render/faqs/