Board Thread:League of Legends discussion/@comment-24603390-20140317093853/@comment-6016076-20140420133239

It's very difficult to generate a general efficiency curve for Last Whisper because it is based on so many variables. It's heavily dependent on the opponent's armor values, on your AD, AS, crit chance, and abilities.

A common goal for creating an efficiency curve is to compare Last Whisper to alternative sources of armor pen in an item build. Compared to BC or YG, it becomes even more complicated.