I went back and retested my content on the N5105 with the "Allow hardware decoder direct rendering" enabled now that the blue line is gone.
I can play back all of my <30fps media (720p, 1080p, 2160p w/ HDR passthrough) using Lanczos 3-taps upscaling, pretty incredible! That's basically ROHQ quality on a 10W CPU
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It starts bottlenecking on 50fps European content, but I only have a few of those files so I'm just sticking with Lanczos 3 taps unless there are any additional crazy performance improvements on the way. I can get away with 4 taps on native 4K content but it drops frames on 720p 30fps so not worth the headache of switching back and forth until performance profiles are ready.