NJ, We only do 6 weekly on domestic work. I find it good. The windows are dirty enough and the custies don't get the impression that you are there every 10 minutes, if you know what I mean. The downside to that is, you need more custies than a 4 weekly round. More custies spread over a longer time is secure. If you lose 1 or 2, then you have time to replace them without it effecting your income.
Do you see what I mean?