The loupe in the contact sheet is a great addition. When using a single monitor and with PM maximized, I think the loupe works in an appropriate manner. If PM is not maximized or if you have a second monitor, it would be nice to be able to define a separate pop up window to hold the zoomed image.
Regarding the zoom feature in the preview window, you might consider adding a Ctrl+Z option to zoom and center the image under the current cursor position.
Deven