The Vortex is a good scope, as are the Bushnesll Elite series (although there customer service is terrible). I would personally stay away from 50mm objective scopes as they require high rings that make a good cheek weld impossible. As far as "power" needed for long shots, the longest shot I ever witnessed was an antelope my dad shot at 550 yards +/- a few. He was using a straight 6x scope and had no problems. He had a friend shoot a large Mule Deer in Colorado across a canyon one year using a 4x scope at what they estimated to be near 700 yards (before rangefinders). Scope power doesn't make up for lack of practice.