I'm not sure why your experience is not lining up with what I have seen. Grafting the earliest possible is great in the sense that you get much better growth. Particularly on apples, there is a huge difference between early and late growth. But if its too early the bark will not be slipping and there will be no good results. For persimmons I have been ruined many times by grafting when there are nice fat buds showing - the bark still was not slipping well and every graft failed.
I am starting to wonder if there is something in the temperature fluctuations that causes the bark to get slipping earlier where you are compared to on the east - we are more consistently cold and you have bouts of really warm weather to get things going. Trees don't revert, once the bark is slipping it stays that way.
The ideal callous temps for peaches is around 55-75F, and unlike most other fruits they callous very little when it gets colder. Still, if the bark is slipping well they will be doing some callousing on days with highs in the 60's.
Obviously if its working for you keep doing it, but I have done many peach grafts exactly when you are mentioning to do it and got near 100% failures. So, there are some things here we don't completely understand; I think it is related to how well the bark is slipping and that is based on temps in the recent past.