XML can be stored as text and as a binary file format.
If your primary goal is to let a computer read / write a file format effeciently you should work with a binary file format.
Databases are an easy to use way of storing and maintaining data.
They are not the fastest way to store data that is a binary file format.
What can speed things up is using an in memory database / database type. Sqlite has this option.
And this sounds like the best way to do it for you.
