Whisk together the honey, vinegar, olive oil, lemon juice, Worcestershire sauce, tarragon, rosemary, garlic powder, white pepper, and salt. Pour into a resealable plastic bag and add the flat iron steak. Squeeze out excess air, seal, and marinate in the refrigerator at least 6 hours.
Preheat an outdoor grill for medium-high heat and lightly oil grate.
Remove the steak from the marinade, shake off excess, and discard the remaining marinade. Cook on preheated grill to desired degree of doneness, about 4 minutes per side for medium-rare.