I went out last week (we have a festival for 5 weekends after the 4th) to shoot my first fworks - turned out to be a bad position, but I spent 3 hours talking to and exchanging info with 2 pro photographers (one has the contract with Busch Stadium for all their "official" shots).
I played with exposure even used settings recommended by several books and was still disappointed - your settings will be what I use next time!.