Great post Anders, it was very useful tonight when I sized the band myself. And it applies to 5165 as well ;-).
Few remarks about speeding things up a bit. I used two sowing needles to hold the band in while checking the fit of the band after each cut. I did not have patience to re-fit the pins after every cut ;-).
I agree that it is important to cut very carefully and take time to check the fit with buckle closed.
Remember to put the watch on your wrist after each cut, close the deployant buckle and see how it aligns. If you use needles be careful so they do not fall out or they don't pinch you.
Second thing I changed - I used small ice cream bowl (sans ice cream) to keep the pins while adjusting the fit. No need for them to roll off the table.
Here is my setup.
And the fit after work is done.
Again Anders great post, thank you for giving me the confidence to cut it myself.