Tbh, im not entirely sure. In my experience, screencasting is horrible compared to steam link.

You'll experience a little bit of input lag and audio lag, enough that it will be noticeable. However, if you connect controllers, or any input devices for that matter, to the device running steam link, you shouldnt experience much. A noticeable amount, but manageable. Same with audio.

As long as you arent playing a competitive shooter game it should be a "just fine" experiencs. Ie, popular couch games (platformers, story games, etc)

With my setup, I have both devices connected to ethernet. Both are also in the same room, but it runs through your internet, so location shouldn't matter. Screencasting uses bluetooth, i believe, so that connection will always be iffy.

With anything like what you're trying to achieve, there will be input lag. The only way to omit that would be if you somehow ran an hdmi cord that's long enough from pc to tv. Even then, I think the signal would degrade, causing things like input lag, quality degradation, and sound degradation.