There's no problem going to northrend pre-70. You can skip one of the two starter zones if you start at 70 so if you start at 68, doing them both should get you up to speed. You MUST get the achievements for those two zones to get back up to pace. Yes the collection quests suck ass, but I've got to tell you that I dinged my first team of 5 to 80 just shortly after a week of release, and within a few days after that I got the Loremaster of Northrend, so I was skipping only dungeon quests. I was about halfway into Storm Peaks when I dinged 80 and I was getting the quest completion achievement in every zone. I ran no dungeons whatsoever.

My second team of 5 took a little more time to level up (they were 70 to begin with) because I was diverting attention to raiding on my first 5.... as a result they had a lot more rested XP. With them, I did Howling Fjrod, Borean Tundra, Dragonblight, Grizzly Hills, I then skipped Zul'Drak and Sholazar Basin and went to Storm Peaks followed by Icecrown. I started the team at 70 and was getting quest completion accomplishments in all the zones I was doing. I was about 10 quests away from the Icecrown quest completion achievement when team 2 dinged to 80... I'm yet to go pick Zul'drak and Scholazar Basin back up, but I need to do that at some point for the rep gains if nothing else.