Hi @jblair, the quoted figure of 55Hz is an averaged value for gaze data capture from the IR cameras whether for one or both eyes. There is no difference in this value whether or not monocular tracking is being used.
In any event, there is no setting within the Eyex (or indeed any other of Tobii Trackers) that would track exclusively one eye.
Please also bear in mind that the long term storage of Gaze Data using the Eyex or 4C Tracker is a breach of the Licence Agreement requires a special licence obtained from Tobii Pro.
More information regarding this can be found @ https://help.tobii.com/hc/en-us/articles/210251205-Can-I-use-a-Tobii-Eye-Tracker-for-research-purposes-