It depends on Temps, sun and variety. Look at the thinning section of the fruit tree guide, you'll see what I mean. Sounds like you read it.
I would probably just try to spray w/ Carbaryl this year and see how you make out. Petal fall and about 10-12mm if needed. Petal fall spray, up to 4 days after petal fall, is a good idea imo. It gives you a week to 10 days to asses. That's normally what I do. Harder varieties to thin ( for me, Macoun. Fuji, and Gala ) almost always need the 2nd spray. There are other thinners, NAA and BA, effective, but they have their timing issues.
The one tip I would really give you that may not be in the book, is that it is hard to over thin using Carbaryl! It's not a real effective spray, but it does work, it will not kill king blossom fruit. It also has the added benefit as a pesticide, so it can be used for that petal fall spray for plum curculio. Like w/ other pesticides, only spray first thing in the morning or at last light so you do not kill bees.
Top worked some trees to Empire this morning. This is all I could do. My Dr. would probably say it was too much but it felt good to do something!