The initial quest gear in Northrend is better then Tier 4.
You'll be replacing Tier 5 by the second zone.
Depends how well geared your Druid is as Feral I suppose.
With WotLK, Feral tanks no longer stack defense, being Crit immune from talents alone.

I'd strongly consider having the Druid as Balance/Resto for leveling.
Balance does not care if follow breaks when melee starts, they can DPS from range.
Balance can DPS as well as Feral, and is a lot easier to multibox a ranged DPS then a melee DPS slave.
Most of the gear is caster gear which is useful to both specs.
With Feral and Resto, you will sometimes take an item great for one and useless for the other.