The only way to clean windows the first time is to clean them all the way round the house, leave for 5 mins then come back and do a glass only clean all the way round the house.
You're washing years of dirt off the frames, so you're not going to get the glass clean in one go.
Always works plus you don't need to spend an age rinsing.
Vin
I agree with Vin,
this is the best way. In fact we did several houses and then came back to the first and did them again glass only. The time delay made sure that they had virtually dried off by the time we started again.
Another issue you will have is that no matter how rigid your pole is, you won't have the strength and experience to aim the brush head so the jets of water don't spray everywhere you don't want them to. This is itself will take time to master.
Slowly does it and don't panick. We managed to get it right eventually with Unger Teleplus poles and Vikan oval brush head - but it took time.
I remember 1 house we still do 9 years later. The front lounge windows wouldn't stop running a milky white - UPVC frames. Thank goodness it was downstairs. But the 4th go I dried the frames down with a cloth and bladed the windows. The next time I went around I expected the same problem and was expecting to loose the customer. The windows were perfect and have been ever since.
Spend time on the first clean and get it right. The second will be easier and the third a doddle. Don't give in. If you think you have a problem with a too higher flow rate then try it a bit slower, nothing wrong with a bit of trial and error.
Personally, 4 is good for me on my Varistream now, although I used 3 for years as 4 was slightly to high. I only use 5 if the glass doesn't sheet well, but on normal everyday cleans I find 5 wastes too much water during the washing stage, although it's great for rinsing. But I use a lot more water on 5 with very little time gain with a quicker rinse.