Thank you for your response!

Removed Nvinject (no efi strings at the moment) and it's back to the original driver. No artifacts, but stuck at 1024x768 and only a single screen.

I was aware that QE/CI wasn't working, but I didn't think it was important for normal desktop use, just for making things look much better. Since neither were enabled, is that what would have caused the artifacts? And if so, should I focus on getting both enabled?