My Pila 168S's are pretty well worn out and all of my 17670's are from dead laptop battery packs, so I won't be doing runtimes with them. I did a few for the hell of it, but I won't be posting them. Maybe if I get some new 17670's to use.
I decided to mark the time until the low power warning kicks in instead of time to 50% brightness because the 50% brightness was is pretty hard to figure out accurately.
This is probably my new favorite Fenix light, and it is also the only Cree XR-E 2x123 light that I know of that will run in regulation on a 17670. I got about an hour on Max with one of my worn out 17670's. When the low power warning kicks in you can just kick it down to a lower level and it will go back into regulation for a while.
So far this light is also the most efficient 2x123 XR-E light I've tested.