Stick with 4 and 8 week cleans. i made this mistake and now my round is taking shape my 6 weekers really are a headache, if say i have 14 houses to do (normal 4 weekers) and it happens to fall on the same day you have to do the 6 weekers it can be a pain having to fit them in, or then having to move them to an easier day.
For me the 6 weekers always nearly fall on a really busy time for me and it means more hassle juggling to fit them in, last month they fell into a week that is full and i had to do them at 7 weeks. I know this isnt a real problem but i like to keep my diary simple and be on time as near as possible, esecially when the weather is good as no real excuse.
Andy