Preheat oven to 450°.
To prepare roast beef, combine first 4 ingredients; rub over roast. Place roast on a broiler pan coated with cooking spray. Insert a meat thermometer into thickest portion of roast. Bake at 450° for 20 minutes.
Reduce oven temperature to 300° (do not remove roast from oven); bake an additional 40 minutes or until thermometer registers 140° (medium-rare) or desired degree of doneness. Place roast on a cutting board; cover loosely with foil. Let stand 15 minutes. (Temperature of roast will increase 5° upon standing.) Cut roast against grain into thin slices.
To prepare sauce, combine horseradish, mustard, and vinegar. Serve with roast beef.