Thanks John, for providing this information about weights and recommendations. I will continue to check things out. The debate I guess is about whether it is worth it to spend the money to save the additional work of lugging my Rancher 455 up and down some tricky terrain when that is not a frequent task (although I am sure I would find other uses for a lighter saw). I imagine this fence walking/clean up work would be about a once a year trek - or maybe twice a year - two trips to different parts of the fencing.
I should add, most of the time what I find would be trees of 4-10", or smaller branches, or 1-2 inch brush (and that not often as once I take it out once it does not come back for awhile). There have been larger trees that have fallen, but I could likely manage with a 12' saw for the few times that would be an issue. And because some of what I have been cleaning up was there because the fence line had been neglected for a while I am guessing there will be less and less of a need for doing this.
Again - thanks for the input.