<This was my report for the 4.8.0-2 kernel> And it still works.
I updated Sid/testing a couple days ago and retested current drivers,
"nouveau" is working with sddm okay but froze with plasma(colorful
lighting bolts). Current nvidia-legacy-304xx is working with XRender
and compositing enabled and I'm good with that, tested on Stretch too,
now I can do clean upgrades and I'm happy. Thank you Debian!
linux-image-4.9.0-1-amd64 is behaving like image-4.8 used to behave
nouveau froze with plasma(colorful lighting bolts). Debian's
nvidia-legacy-304xx-driver is freezing with plasma start.
On first boot plasma loaded the vga driver giving me the wrong screen
size and did not load the installed nvidia driver at all. Booting
linux-image-4.9.0-1-amd64 and reinstalling nvidia-legacy-304xx-driver
crashed plasma and so did nouveau. I'm back to using
nvidia-legacy-304xx-driver and linux-image-4.8.0-2-amd64 with XRender
and compositing enabled.