Never dealt with 765, but a lot of 500KV. Minimum approach distance on 500KV is 25 feet, which means it is possible but not likely that it could arc over under that distance if something conductive is in the area. I will say, walking around a 500KV transmission yard in fog or even just really high humidity, the hair on your arms stands up and you can feel a slight tingle at times and that's at 30+ feet above. That being said, I've been on the end of a fire hose on a live 500KV fault at 30 feet or so and been fine, but you have to have a lot of trust in your nozzle and it's not really something you look forward to doing.