We have some windows at 80 feet but only about 30 or so it’s a lot harder work especially with the slightest breaz, after I’ve done that I have a little break , working at 60 feet I would say it depends on the type of windows are they deep recessed or like office blocks with all windows in a line that you can slide the pole onto the next window , I wouldn’t want to do more than 30 - 45 muinets at a time at that height we take it in turns Do a bit each be very careful in the slightest of breases unless it’s a deep recessed window as there might be no wind on the ground but at that height there probably will be , it’s easy to get caught out with the wind blowing one way on the ground and at 60 feet it can be blowing the opposite direction one the pole starts going it’s very difficult to stop it if this happens all you can try and do is stick the brush into a corner of the window and make sure that you are stood directly in line with the top of the pole at all times , hope this makes some sense