Whisk together honey, vinegar, olive oil, lemon juice, Worcestershire sauce, tarragon, rosemary, garlic powder, white pepper, and salt in a large bowl until well combined; pour into a resealable plastic bag. Add flat iron steak; coat with marinade, squeeze out excess air, and seal the bag. Place in the refrigerator to marinate for at least 6 hours.
Preheat an outdoor grill for medium-high heat and lightly oil the grate.
Remove steak from marinade; shake off excess and discard marinade. Cook steak on the preheated grill to desired degree of doneness, about 4 minutes per side for medium-rare. An instant-read thermometer inserted into the center of steak should read 140 degrees F (60 degrees C) for medium-rare doneness.
