I believe what note 6 is saying is that when a current factor is increased by 10, then the max distance of that cable is decreased by 10. As well note six is used when you cannot find a value from the charts. Also, 600V will have less voltage drop than you think. A good rule of thumb is for every 100 feet of conductor, go up one size. But to be acurate, just use the example in note 9 but insert 600 V as the divisor or you will get the wrong answer. If that still doesn't help you, just call the inspector.