I notice the Field of View (FOV) degree per street view zoom level is different between browsers
I believe the documented street view zoom level to FOV is
It is not direct answer to a question, but maybe it helps:
There is undocumented option of google.maps.StreetViewPanorama class named 'mode'. You will be able to force rendering mode, and FOV should be the same for eg. 'html5'
Google Maps API custom Street View quality issue