I agree Ewan, I think prioritising as you have outlined sounds like a good strategy for increasing work speed and turnover.
This is something I will give more thought to.
I usually give equal attention to all parts of the frame and sill and have always prioritised the finish of the glass. With exception to frosted bathroom windows which just get a quick scrub and rinse with brush on (other windows I rinse off the glass).
I would usually clean a property of the size you mention in around 8 to 10 minutes with full attention to all of the frames, sills and glass.
I reckon by prioritising and cycling the cleaning of parts of the frame as you have mentioned I could reduce this by a fair bit where possible.
If I could even manage a 25% to 50% time saving on that I would be well happy.