Heat oven to 425°F. Make pie crusts as directed on box for Two-Crust Pie using 9-inch glass pie plate.
Peel peaches and cut into 1/2-inch-thick slices; cut slices in half. In large bowl, mix brown sugar, 1/3 cup granulated sugar, the cinnamon, flour and salt; add peaches and stir to coat. Immediately spoon peach mixture into crust-lined plate; dot with butter. (Do not make mixture ahead or it will become too juicy.)
Top with second crust and flute. Brush top with egg; sprinkle with 4 1/2 teaspoons granulated sugar. Cut slits in several places. Freeze pie 15 minutes. Meanwhile, heat 15x10-inch pan in oven 10 minutes. Place pie on hot pan. Bake on lower oven rack 15 minutes. Reduce oven temperature to 375°F; bake 40 minutes. Cover loosely with foil; bake 25 minutes longer or until juices are thick and bubbly. Cool 2 hours before serving.