I recently switched from doing both kill and collection quest to only doing kill quests or really simple collection quest (like pickup one of bla bla).... it's SO much faster doing only kill quests in outland.

I haven't boosted my toons through any instances so I couldn't say if thats faster than questing.

I hit outland at 58 nearly 59 and im now 63 nearly 64 and I have done Hellfire, zangra marsh and most of terokkar forest....

Im running a full group of toons and one shot everything.