I believe keeping the mobs at only +2 or -3 of your level is very important for ease of running and the exp loss.

I am not too worried about running around to much, with training spells, vendoring, few easy dungeon quests (way worth it), and mailing to bank alt. I figure jumping around wont be too bad.

My problem is I arrive at WC at 18 but have so much training at 20 I feel it is a definite waste to leave so trying to arrange it differently. I plan to leave WC for SFK at level 22.