Besides the number of greater features that sunshine has added, are there any performance benchmarks to compare the two? Like for 4K HDR @ 120Hz in terms of latency or efficiency in the graphics capture pipelines? Always figured Nvidia could be leveraging their proprietary driver APIs more effectively given they can optimize and control the entire graphics pipeline, end to end.
Any secret sauce Nvidia uses would be in taking shortcuts to capture the screen and send it directly to the encoding timeline. The time it takes to do this without any secret sauce is negligible compared to the two slowest processes in the pipeline: video encoding and sending the data over the internet.
Sunshine is actually often more performant than Nvidia due to improvements in the slower parts of the pipeline.
Here are some discussions on the topic: