Cityman:
Funny you ask- I happened to be talking with Bonilee with FTF this afternoon. They use two main rootstocks for peaches/plums/apricots: Halford and Guardian. I asked her if they have noticed a bloom difference between the two and she had not, though the have observed that Guardian is slower to get going but more precocious overall.
Sounds like this will be a fun experiment- I know I am North of you, but maybe we can normalize our bloom dates around a common CV/rootstock and see if any patterns emerge.