For streusel topping:.
Stir flour, oats, sugar, and salt in medium bowl. Add butter; rub in with fingertips until mixture holds together in moist clumps. Mix in pecans. DO AHEAD: Can be made 1 day ahead. Cover; chill.
Blend flour, sugar, and salt in processor 5 seconds. Add butter and shortening. Using on/off turns, blend until mixture resembles very coarse meal. Drizzle 3 1/2 tablespoons water over. Blend until moist clumps form, adding more water by teaspoonfuls if dry. Gather dough into ball; flatten into disk. Wrap; chill at least 1 hour. DO AHEAD: Can be made 1 day ahead. Keep chilled. If necessary, soften dough slightly at room temperature before rolling out.
Roll out dough on floured work surface to 14-inch round; transfer to 9-inch deep-dish pie plate. Cut off all but 1/2 inch overhang. Fold overhang in; crimp edge. Chill crust.
Stir sugar and next 4 ingredients in large bowl. Mix in lemon juice, then peaches; toss. Let stand at least 20 minutes, tossing occasionally.
Set rack at lowest position in oven. Slide foil-lined baking sheet under rack onto oven floor (to catch any drips). Preheat oven to 400°F Spoon filling into crust. Scatter topping over, breaking up large clumps.
Bake pie 30 minutes. Reduce oven to 350°F; bake until juices bubble thickly and topping is golden, covering edges with foil if browning too quickly, about 1 hour. Cool on rack at least 1 1/2 hours. Serve warm or at room temperature.