I just finished Outland with my first character at level 80. Should I lock the character level and continue onto Northrend or continue levelling in Cataclysm/Pandaria?
Personally, I would move along and go to Pandaria. Then when you want a change of pace, level an alt through Northrend & Cataclysm. With the XP boost right now, you’ll probably outlevel zones pretty quickly regardless. You can also go back at max level to finish off Loremaster, if that’s your goal.
It’s really about preference. If you aren’t in a hurry to get to max level, there’s no harm in doing Northrend now. It’s obviously not the efficient way to level, but it’s a game, so efficiency only counts if it helps you have more fun. If you are enjoying questing and seeing the story, I’d head over to Northrend. If you’re starting to get a bit bored with questing, then focus on efficiency and head to Cataclysm. (I feel that Cataclysm is more efficient that MoP for quick leveling as it’s a lot more on the rails and the zones feel more self-contained so it feels easier to move on even if you don’t finish all of the zones. MoP is still a fair bit more efficient than BC or Wrath for comparison, though.)
If you do decide to go onto Wrath, I probably wouldn’t bother level locking for it. (At least not at first.) Things won’t get any easier until the overlevel bonus starts to kick in at 85, so you won’t be blowing through mobs for the first few levels. (And XP gains drop pretty quickly after 81, so it will be a bit before you have to decide if you want to stop XP before you hit 85.)
For Cata/MoP content, you won’t start getting the overlevel bonus until 99, so again, you’ll have several levels of reduced XP before you have to start worrying about things getting trivial. WoD’s bonus starts at 109.
I would definitely lock XP at 109 if you haven’t hit Legion content yet at that point, as the BfA intro automatically becomes available at 110 causes phasing issues for the Legion and Cataclysm zones intro quests. (Those phasing issues clear up once you’ve actually done the BfA intro stuff, but it forces you to do stuff out of order.)
IMO its better to go the most efficient route while we have this 100% exp bonus until 4/20. Almost everyone has multiple characters so you can send more characters through extra zones you miss later or even now simultaneously.
80-90 dungeons are very good and you’ll get quests in the dungeons…world quest while in queue. I think WoD 90-100 is fast and great questing. In general, questing is better than dungeons from 90-120 unless there is a time walking dungeon event. Ironically, time walking starts tomorrow for a week. i have my last three non 120’s (110’s) waiting to speed level through dungeons to 120. Timewalking + 100% exp will be light speed leveling.
If you are doing anything with professions, Northrend professions will produce gear for the level 70’s, Pandaren professions, gear for 80-85.