For those of you looking for something more than stock, something faster with a ton more customization, definitely check out the latest version of Pure Nexus ROM for your Nexus 6P.
Based on latest Android 6.0.1 r10, Pure Nexus ROM brings you pure experience of Google OS along with excellent choice of customization options. For T-Mobile users, you will also get WiFi calling working out of the box. It also has fully working VoLTE and for Sprint users it has native support for PRL/Profile update.
Inside PureNexus Settings, you will be able to fully customize your lockscreen,notification drawer, recent apps, status bar, navigation bar, power menu, display, and much more. But what I really like about Pure Nexus ROM is its raw performance and stability like stock firmware.
Overall, this is certainly one of the best custom ROMs you can enjoy on your Nexus 6P so definitely flash it over this week(end) and do let me know what you think!
You need a rooted Nexus 6, if you do not have a rooted Nexus 6, see How to Root Nexus 6P first!
You will need to update your bootloader to the latest MMB29P or later, you can follow this guide. (Or you can do this if you end up in a bootloop.)
For installation, simply reboot into recovery, format /system and /data, then install ROM, and Gapps. You can try installing without wipe if coming from stock firmware but make a backup ROM beforehand.