In small bowl, whisk together mustard, vinegar, soy sauce, honey, garlic, salt, pepper and cayenne pepper. Cover and let stand at room temperature for at least 1 hour to blend flavors.
Trim meat if needed and cut into 1 1/2 inch pieces. Transfer to large bowl.
Spoon half of mustard mixture over beef; toss gently to coat. Place in zipper plastic bag and marinate for least an hour in the refrigerator.
On 10-inch skewers, thread meat, leaving 1/4 inch between pieces.
Reduce heat to medium (on a gas grill). Place meat skewers on grill rack over heat. Cover and grill 8 to 10 minutes or until meat reaches desired doneness, turning once and brushing with remaining mustard mixture halfway through grilling.