Hi @henryrh, unfortunately your question is rather outside the scope of this forum as we have in place a premium supported VR solution called Tobii Ocumen which is indeed setup to provide customer the kind of project solutions that you are looking for. You can read more about Ocumen @ https://vr.tobii.com/sdk/solutions/tobii-ocumen/
However, perhaps you have already noticed that Ocumen does not support the HTC Vive Eye Pro, so I will try to assist you best I can with your current question.
Our sense is that the update loop frequency is determined by refresh rate of application so it would be better to start a separate thread for your application. Ideally you want to be capturing data quite separately from the FPS setting in Unity. Try a separate thread and adjust the FPS setting to see if that is indeed impacting the final frequency of gaze input and let us know the results.