I just wish project Fi would release the factory rom they use on their n6s. They stated it was the same but with minor tweaks for project Fi
I installed the Fi ROM (LVY47H) from http://xdaforums.com/nexus-6/development/fxz-nexus-6-recovery-flashable-fastboot-t3066052. Has been working great for me.
The main tweak between this and any others is that the Project Fi app is part of the system on this (so it can't be uninstalled, and it starts the Fi activation as part of the onboarding when it's first turned on or after a factory reset)
But yes, I agree it's lame that they still haven't released the image directly on https://developers.google.com/android/nexus/images :/