So i just finished leveling as Holy the entire way 1-60. I managed to clock in at 9 days 10hrs played. However i also have 300 Fishing/Cooking/First Aid and 290 Engineering and like 285 Mining when i hit 60.
I will speak from experience, Up until say High 40s its not to bad to be honest, however once you get into 50s the time to kill goes up alot. I am talking anywhere from 30s to 90s per mob. I would not recommend killing yourself trying to level as holy, but if you do, make sure you have some patience :)