I'm no engine expert, but there isn't much difference between flooring the gas pedal whether it's in 1st, 2nd, 3rd, 4th or 5th, end of the day, you are thrashing the balls off it (in a matter of facts, it's less damaging in 5th as the max rev in top gear is usually lower than the rest).
Just think boy racers, who redline the engines all the time, would you buy any car off them?