Magic Missiles has a 3 second cooldown so extra missles are quite impactful, and I'd like to have my Missiles and Arcane Orb with similar ranges. If the enemy team has 2 or more divers (ex. Illidan/Kerrigan), then the extra range would prove to be quite useful. In the end it is kind of down to personal preference, but I find the 2 extra missiles to be amazing poke damage. I just feel the extra range is unnecessary if you are taking talents at level 4 and 7 to reduce the cooldown of Arcane Orb...