I dont know whether anyone is using those leveling classguides and you want to keep them updated. If someone does we should really recommend him or her to use Protection instead of any other spec. When questing you are about 20 - 30% higher in dmg and your shield slam is one hitting in leveling gear at least up to level 40. Normal mobs never got me a third hit untill now.
In dungeons played as damagedealer in tankspec you are about 10% higher then both damagespecs - as a tank you are using revenge nearly without anything between because you are likely to parry again and again starting from groups of 3 adds hitting melee. (Remember to glyph it asap
I am at level 54 now. Never visited any dungeon in tankspec doing less then 65% of overall damage. closest behind is warriordd but even in leveling gear it is far far behind.
I dont want to make it a self-adulation. Its just only my own experience I can present