Forgot to mention: in the kern.log attached above, there are some new messages with the 4.8.0-rc2 kernel that weren't present with 4.4.0-31:
Aug 15 18:47:06 panzer kernel: [ 310.233191] [drm:drm_atomic_helper_commit_cleanup_done [drm_kms_helper]] *ERROR* [CRTC:26:pipe A] flip_done timed out
These appear numerous times, in addition to the 'vblank timed out' messages and associated stack trace, which also appeared as before.
Forgot to mention: in the kern.log attached above, there are some new messages with the 4.8.0-rc2 kernel that weren't present with 4.4.0-31:
Aug 15 18:47:06 panzer kernel: [ 310.233191] [drm:drm_ atomic_ helper_ commit_ cleanup_ done [drm_kms_helper]] *ERROR* [CRTC:26:pipe A] flip_done timed out
These appear numerous times, in addition to the 'vblank timed out' messages and associated stack trace, which also appeared as before.