If I wanted to know how long a MouseMove took I'd more than likely test it with something like this.
Sleep(1000) ; give interpreter some time to wind up
MouseMove(0,0,0)
$Speed = 20
$Distance = 100
$Timer = TimerInit()
MouseMove($Distance,0,$Speed)
$TimerDiff = TimerDiff($Timer)
MsgBox(0,"Speed Per pixel at " & $Speed ,Round($TimerDiff / $Distance,2) & " Milliseconds")
Exit
If I wanted to know how it is implemented in Autoit I would consult the last source available.
Also, I don't take sides, right is right and wrong is similar.