In the Contact Sheet you can set Cursor mode to Loupe, and then when you click on a thumbnail, you get a zoomed view that is centered where you clicked. Could there be something similar in the Preview window?
I understand that you can hit Z to zoom in the Preview window, but this zooms in to the last zoomed position, which means you often have to drag the image to see the part of the photo where you need to check sharpness. Could there be a mode or setting where instead of using Z to zoom, you use the mouse to click on the image, and the zoom is then centered where you clicked? This could potentially save a lot of dragging.
