I appreciate all the sentiments. The large data sets are still CSV-based, but I have need to start storing more information such that the data is no longer flat. XML seems like an ideal mechanism (or possible a set of datbase tables), but I'm very concerned with speed. The current implementation is not the speediest and any real slowdown is going to be noticed.
I control both the reading and writing of the files, and I thought it would be ideal to use a subset of XML (for speed).
Allan