5-boxing "old" instances while leveling?

[Rigz]

I think you should do them.

Running quests is mostly 1 shotting stuff. but inside instances u really learn how to act with 5 characters, paying attention to healing. mana. targetting. etc etc.

This of course is a personal opinion. I have only been doing instances seriously since lvl50, before that I boosted myself.

I agree with this. There is no doubt you are going to level faster questing, but there is a certain satisfaction to doing the 5 mans yourself, also they help keep you better geared as well. I would say stop to do one every 10 levels, don't do every single one if speed matters to you.