I've been using the arb for the past month or so and I fricking love it.
Its definitely not something I use against peasants though. I aim for archers first and foremost. I can usually one hit them if they're in really low armor. Most archers survive one shot with decent armor but they're most likely blackbarred at that point.
Then you help in melee and shoot peasants.
The only thing I hate with the arb is the slow reloading time (which is fine) but it sucks when you're on open plains and being targeted by an HA/HX/archer. My god the frustration.
Ill shoot at anyone as long as they are running in a straight line... It's the ultimate archer killer though. I just see archers as some kind of prey to be stalked and killed...
One good tip for any other high ath snipers out there; when some melee guy starts chasing you, hit qfm continuously, ("follow me!") usually pisses them off enough that they give up the chase