How would you set item level requirements for Leveling Dungeons?

[Barraind]

The problem with that is the vendor gear at NQ is easily surpassed by lower ilvl gear at HQ stats. Bardam is the first dungeon in SB that starts to shell out some damage. Let's say you bought i279 vendor gear, as you could be lv66. The augmented Shire gear at i270 will still beat that by quite a margin. The vendor gear has a bit more Def and MDef, but not enough to make it better.
Quests give you vendor geat at HQ, but they are not repeatable and they are often expensive on MB.

Tank 270 vs NQ 279:

NQ has ~25% more of each defense
Shire 270 has ~10 more str and ~50 more vit.

The NQ stuff is significantly better on a tank, its not even close.