I agree with Squeaks on the method for doing them trad, it is quick and it does a good job.
Nonetheless you have to beware of going to fast, on leaded in particular, faint smears can be left behind that will show up in direct sunlight.
The average window with WFP will take somewhere around 30/40 seconds to do, it is very unlikely you can trad clean a window that has 3 standard size casement style leaded panes.
And I would be more than happy to stopwatch someone such as Squeaks doing them trad, perhaps Roger should stopwatch himself...he might be surprised, I would doubt he would do a window such as I have just described in under 40 seconds...it might feel really quick, but it will be longer than that.
Plus of course the quality of the clean has to count too.
The 30/40 seconds I've allowed for WFP is also a very generous timescale, and anyone using WFP would clean such a window in that time with ease.
And on upstairs windows trad would be slower again due to climbing and moving the ladder if nothing else.
another point to consider if spraying and buffing is even faster than using a squeegee on a similar non leaded window...why bother using a squeegee at all?
The answer is easy of course, the squeegee is faster and does a better job, were you to use this method on normal windows you would get smears all over the place.
but failing WFP, a proprietary brand of window cleanig spray (Tesco's own brand is I think the best, and cheapest to) and a microfibre cloth is the next best way of dealing with leaded windows.
Ian