BarbiesBoyfriend - has this figured out. I always carried 5 to 10 knots extra speed "just in case". When are you 'professional' pilots going to realize this is NOT an exact science?! I don't care how many thousands of hours one has. Most of that time for 'heavy' drivers is in cruise anyway.....means nothing. It's the time below ten thousand feet "where the action is" that really counts.