Sorry but the theory about killing light blues to level items faster is 100% false. ALL of my evovling items have leveled fastest by killing QUALITY mobs over quantity. For example, my cloak of the spirit tracker typically will gain 10% of a level for every 69.1 HARD mission I do, which consists of high hp, red drachnids. By contrast, I went over to grieg's end, and killed non-stop solo for over 2 hours straight, and gained less than 5% of a level on the cloak.
The amount of exp the mob gives plays a big role in amount of time it takes to level an item - exactly as it is for gaining regular or aa exp for players. THAT is the truth about evolving items.