GPT + zfs root, manual installation, gpart -p /boot/boot.efifat -i 1 ada0, as per manuals.
Boot works fine, graphical quality of UEFI console are excellent (compared to vt console).
1) Console goes BLACK and boot never completes if nvidia-modeset driver is set to load via /boot/loader.conf (nvidia-modeset_load="YES").
Solution so far: NOT load the driver at boot time via /boot/loader.conf but `kldload nvidia-modeset` manually after boot.
NOTE: this does NOT happen on VT console.
Another thing I've noticed: on one of my systems using UEFI, but not on the other (I have two), shutdown doesn't work well when booted UEFI. After shutdown & halt it reboots after a few seconds. Not like "reboot", when it reboots immediately -- but it halts, then boots up again after a few seconds.
With VT console non-uefi boot shutdown works fine. The problematic system is Huananzhi x79 2.49PB (Luxury): LGA2011, Intel Cougar Point C206 etc.