If you have 99 wpf, your weapon does 99,85% of weapon damage and if you have a 100 wpf it will do a 100%. Try the formula again and make sure you use 0.85 instead of 85. The progression is constant, which means that the difference between 90 and 100 wpf is the same as the difference between 100 and 110. So no need to worry about reaching that magic 100, because there is nothing magic about it.