yup

Four-hundred pixels is clearly the maximum width when selecting the Large image upload option. You can see the ratio at work here. Look at the text and see how it is crunched a bit. You can see it in the numbers, 420, 450, 480, 500, getting smaller and smaller as Blogger constrains all of the widths to 400. Click on each line below to see the full size. Well, now I know. Back to Photoshopping.