NPC and aggro radius

[det]

I remember a long time ago, when doing the Hecular rod quest where you have to bring an item from Tarren Mill to Southshore GY, that the guards would aggro me (lv 38) from extremly far away. Somtimes even across the river that runs to the sea there.

At lv 48 however, my son (Troll) could pretty much stand inside the Griffonmaster (Dwarf) at Tanaris.

The patroling lv 45 (?) Tauren in STV doesn't seem to attack even players who walk through her, while the 4 lv 25 elite Alliance Outriders seem to spot and kill other players fairly easy.

Any idea how the aggro radius works on those? Does attacking guards or PvP flagged NPCs always automatically flag you for PvP while ebing attacked by them does not?

What is the experience if you (as Alliance) try to get to Tanaris / 1000 Needles. Do the guards (lv 30) at the great lift aggro easily, or are they more of a "decoration" ?

[Aerath]

Some are simply set to 'non-aggressive', such as the tauren in STV or Rexxar in Desolace. They won't act until attacked. Griffon Masters don't attack either until attacked.

The guards @ the Lift will aggro if you are in their level range - if you're high enough to go to Tanaris (which is likely the reason you'll be passing them as allilance), they won't be a hassle.