Generally, line post spacings will range from 20′ to 50′ and should be based upon the slope and lay of the land. In most level areas 40′ to 50′ is a good distance. Out west, you will see spacings of 100′ or more.
The closer your spacings the more visible your fence will be. So if aesthetics are important to you, and you want the fence to look more “fency” then narrow your spacings.
A mix of wood posts and PasturePro post is also an appealing and strong fence. In this case, you could put a wood post (4″ or 5″ diameter) every 300′ to 400′ then use 6 to 8 PasturePro posts between. This will give you a strong, attractive and effective electric fence with very little maintenance requirements over its lifetime