Cut steak into 4 equal pieces. Cut 2 garlic cloves in half, and rub both sides of each steak with garlic. Place a large nonstick skillet or grill pan coated with cooking spray over high heat until hot. Add steaks; cook 4 minutes. Turn steaks, and cook 3 minutes. Reduce heat to medium; sprinkle steaks with 1/4 teaspoon salt and 1/8 teaspoon black pepper. Cook 2 minutes or to desired degree of doneness.
Mince remaining garlic clove. Combine garlic, sour cream, mayonnaise, horseradish, 1/4 teaspoon pepper, and remaining 1/4 teaspoon salt. Serve steaks with horseradish sauce.