Completing the Wrath Gate sequence will also irrevocably phase you into a different version of Azeroth where some NPCs are no longer around. Think about this whole phasing deal for aion gold, because it looks like it will be pretty exciting in the near future. They are essentially the same in terms of number of quests and mobs, so generally the experience gain rate would be the same. But that is alright, those guys are self-righteous, anyway, and a true servant of the Light can not be distracted by some silly animal rights crusade! Of course, the reality is that the Borean Tundra also gives prettier shinies, such as the Axe of Frozen Death for leveling Retribution Paladins.
The flying will not be particularly useful to first characters, but will be extremely useful to alts whose Level 80 main characters can purchase the Tome of Cold Weather Flight, an account-bound consumable book.