Of course the only way to know what your bullet speed is would be to chrono it. The book load is an average/estimate of what you will achieve. 2 inches shorter could actually be faster than what you are guesstimating for the longer barrel. Usually FPS loss is roughly 30 FPS/in depending on who you ask.
Here is a calculator that can give you some idea of what you are doing, but without actual measurements, the only way to know is to shoot at those distances.
http://www.handloads.com/calc/
