Boeing want you have taken the 1st action to stop no later than V1
With a fire before V1 I will stop. Having lost a friend to an airborne fire I have no desire to take an unecessary risk. Structural failure may occur as early as 4-5 minutes if the fire is uncontained and spreads. I do not practise turnbacks (onto reciperical) mvrs in the sim but I do practise stopping from V1 or below. The sim conditions you to fly a pattern back to land you may not have the luxury of that time as has been tragicaly proven several times.