I'm going to make a bosun's chair to lift me 40 ft in the air to a tree platform (with at least a 6' clearance, so closer to 50'). Of course I would like the right type of rope with the right tensile strength.
It might be useful to have a second line in case of the first one snapping, but the primary one would be for lifting and not falling.
Of course there will be pulleys involved so the rope needs to be able to make bends without degrading.
And it will remain outside most of, or almost most of the year in a climate with snow and ice and temperatures down to -20F once in a while; usually in the 10s and 20s in the winter. There will be sunshine typical of the temperate zone though the rope should be undercover in the growing season. The working load will probably be about 200 lbs., not counting the weight of the rope itself.