Bread Pan Sizes

You have a good eye...the size you have is a loaf pan designed for a 1.5 lb hunk of dough, rather than the slightly smaller 8.5 by 4.5 made for a 1 lb loaf. You can put a smaller loaf into the bigger pan with no worries, but the larger amount in the smaller pan will yield a loaf with a huge mushroom to and/or collapse. In something like a pound cake or banana bread, the batter will overflow terribly if the wrong sized pan is used.