Twin 4040's a bit ott for the average setup though I would think.
why be average ?
Trying to be clever as always Ian and go one better. He asked a simple question and got some simple helpful replies.
It doesn't mean he's an average window cleaner. It means that in my opinion a single 4040 would be more than sufficient especially bearing in mind some peoples RO Man setups or similar. He could add another 4040 at a later date if he wished.
I'm sure though a single 4040 is fine for a one man band or even if you had an employee. If he was bigger than this then I don't think he'd be asking the question.
Also I'm sure like most of us he would have an eye on cost and an extra 4040 would be £300