FYI

From the Boeing manual - this is for the 707, 727, 747, 767 & 757.

For every knot of extra airspeed add 50' to the landing distance. Ten knots fast would take 500' feet more runway.

Also, you would add 1/2 the gust to the VREF  Ex. - 250/15 G25 you would add 5 knots as a pad to the approach airspeed.

Lou