I recently posted this on the steam link forums but have not had a response, I don't know what relationship you have with valve and how your product is integrated into the link but hopefully you can help
Since updating to steam link beta 518 I have noticed a large performance regression with device streaming of my G27 wheel in both iRacing and Project Cars (the two games I have tested). It appears when applying steering input (and therefore receiving force feedback for the centering forces I believe) the decode time goes through the roof (a jump from ~20ms to ~120ms average with massively high peaks) causing frame jitter and high latency.
The following images demonstrate the problem. The red graph represents the frame decode time for the steam link (as far as I can tell)
Captured driving on a straight, minimal wheel input, latency is slightly higher than for a game not using device streaming but not out of this world
Captured after performing a series of weaves, notice the really spiky decode performance, massively high latency and frame loss
This has definitely regressed since previous versions where the device streaming worked flawlessly. This is the first version I have tried with the non free steam app, but it's quite hard to diagnose the issue. Unfortunately it has rendered the virtual here feature of the steam link broken for me as the main reason I bought it was to use my wheel with the link.
I understand this might not be your issue but I thought it worth reaching out anyway.