Heat oven to 325°F. Combine Ancho Rub ingredients in small bowl. Reserve 2 tablespoons rub for potatoes. Press remaining rub mixture evenly onto beef roast.
Place roast on rack in shallow roasting pan. Insert ovenproof meat thermometer so tip is centered in thickest part of beef, not resting in fat. Do not add water or cover. Roast in 325°F oven 1-3/4 to 2 hours for medium rare; 2 to 2-1/4 hours for medium doneness.
Remove roast when meat thermometer registers 140°F for medium rare; 150°F for medium. Transfer to carving board; tent loosely with aluminum foil. Let stand 15 to 20 minutes. (Temperature will continue to rise about 5°-10°F to reach 145°F for medium rare; 160°F for medium.)
Meanwhile combine reserved rub with oil in large bowl. Add sweet potatoes; toss to coat evenly. Place potatoes on metal baking pan sprayed with cooking spray. Cover with aluminum foil and roast for 1 hour. Uncover potatoes; stir and continue roasting 10 to 15 minutes or until tender.
Carve beef roast into thin slices; serve with potatoes. Season beef and potatoes with salt, as desired.
Nutrition information per serving: 472 Calories; 126 kcal Calories from fat; 14 g Total Fat; 4 g Saturated Fat; 5 g Monounsaturated Fat; 15 mg Cholesterol; 139 mg Sodium; 36 g Total Carbohydrate; 6.1 g Dietary Fiber; 50 g Protein; 5.9 mg Iron; 9.7 mg Niacin; 1 mg Vitamin B6; 2.6 mcg Vitamin B12; 8.6 mg Zinc; 53.7 mcg Selenium;