Well, that “Edit Image” gives more control but you have to edit every single image. If you just want to do it automatically then Page Header Image is better. You can just upload image of whatever dimensions and tell it that you want resize it in Page Header to some specified dimensions and it’s done for all images at once.
Page Header – Image
1) No, I tried and it didn’t resize proportionally.
I took large image, enabled Hard Crop, set Image Width to 500 and Image Height to 0. This happend: http://www.foxtrot.me/test-post-1/
And even if it worked somehow I think that resizing just by width isn’t ideal.
For tall images height is more important. So there should be some way to set just height and width would be calculated. If even after resize that image would be wider than site’s content container than it would use width of container and calculate height of that image so it would fit the container.
I tried (with tall image), set width to 0 (it was then automatically set to 1200), height to 500 an this happend: http://www.foxtrot.me/test-post-3/
I know that I could just edit every image in that wordpress tool but I like better this option that resizes every image automatically.