Preheat oven to 350°F. Prep jumbo muffin tins with wrappers (or spray with nonstick baking spray). Set aside.
In a large mixing bowl, combine sugar and oil, stirring well.
Add eggs, mixing well.
Stir in pumpkin. Mix thoroughly.
Combine all dry ingredients in mixing bowl, and add to pumpkin mixture, alternating with water.
Stir in vanilla extract (and pecans, if using).
Dish muffin batter into prepared pan using a #10 disher. If using a spoon or measuring up, fill each muffin tin cup about ⅔ full.
In a small mixing bowl, combine all streusel topping ingredients. Mix with a fork until well combined and crumbly.
Top each unbaked muffin with 2 Tbsp of streusel topping mixture. Gently pat the topping with your hand to help it stick to the muffin.
Bake muffins at 350°F for 30 minutes or until a toothpick inserted into the center comes out clean.
Cool muffins for about 10 minutes in the pan, then transfer to a wire rack. Cool completely.