Remove giblets and neck from turkey. Reserve turkey neck; refrigerate, covered, overnight. Place turkey in a 15x10x1-in. baking pan, breast side up. Secure skin to underside of neck cavity with toothpicks. Mix salt, sage and garlic powder. Tuck wings under turkey; tie drumsticks together. Pat turkey dry. Rub outside of turkey with salt mixture. Refrigerate turkey, loosely covered, overnight., Preheat oven to 475°. Place onion, celery, carrots and reserved neck in bottom of a broiler pan; add 1/2 cup water. Place broiler pan rack over top; transfer turkey to rack. Rub outside of turkey with oil; sprinkle with pepper. Pour wine and remaining water into turkey cavity; add sage and thyme sprigs., Place turkey in oven, legs facing toward back of oven. Roast, uncovered, 40 minutes., Reduce oven setting to 350°. Cover breast tightly with a double thickness of foil. Roast until a thermometer inserted in thickest part of thigh reads 170°-175° (thermometer should not touch bone or fat), 1-1/2 to 2 hours longer., Remove turkey from oven. Let stand, uncovered, 20 minutes before carving. Using a turkey baster, remove liquid from turkey cavity to a large measuring cup. Line a strainer or colander with cheesecloth; place over measuring cup. With a slotted spoon, remove vegetables from bottom of broiler pan, reserving 1-1/4 cups. Discard turkey neck. Strain cooking liquid into measuring cup. Skim fat, reserving 1/4 cup fat. Add enough broth to the cooking liquid to measure 2 cups., In a large saucepan, mix flour and reserved fat until smooth; gradually whisk in broth mixture. Bring to a boil over medium-high heat, stirring constantly; cook and stir until thickened, 1-2 minutes. Add half of the reserved vegetables. Puree gravy using an immersion blender; or cool gravy slightly and puree in a blender. Stir in sage, pepper and remaining vegetables; heat through. Serve with turkey.