The most important factor in the strength of a strained fence is the straining posts.
They take all the load of the strained wires, and the intermediate posts are only there to stiffen the fence, and to hold the wires at the correct height from the ground.
Wire should be attached to a running fit at the intermediate posts, so that any extra load, for example from an animal leaning on the fence, is transferred along the length of that strain.

Round peeled and pointed posts are generally stronger then the equivalent machined round posts, due to the varying diameter.
Although less attractive than a machined round post, they are much sturdier and so are typically used as field posts, or in places where aesthetics are not the issue.
They are also more economical than machined round posts