Cook and drain macaroni according to package directions.
Preheat oven to 350ºF. Butter a baking dish or coat with nonstick cooking spray and set aside.
In large saucepan over medium heat, melt butter. Sprinkle flour into butter and whisk constantly until you have thick, smooth paste, about 5 minutes.
Add mustard, red pepper and Worcestershire. Gradually whisk in milk and continue stirring until sauce thickens and returns to simmer.
Reduce heat to low. Add 3 cups of cheese and stir until melted. Add macaroni, stirring until well coated. Pour into prepared baking dish. Sprinkle remaining cheese evenly over top, followed by crumbs. Bake for 20 minutes, or until golden on top.