I can't really speak on TBC but in azeroth I leveled several teams.. Started dualboxing and later added 2 more.. my teams that I leveled dual boxing finished to 60 faster than my quad group. I hit 60 in felwood with leftover quests.. and my quad group hit 60 in winterspring. I would do the 2x group .. and then meet up at 60 to go from there. My guys all ran the same quest pattern from 34-60. Up until 34 they were all instance boosting.