How to efficiently update an XML file with Repeater items?

[CRAY-T3E]

I'm binding an XML file to a repeater, each item in a textbox. When the Save action is triggered, I need to write the changes back to the XML file. My question is what's the most efficient way of doing this, bearing in mind that the XML file is very small. I can think of three, and I don't know which is best:[*]Loop the repeater, find the matching ID in the XML file, update those nodes[*]Loop the XML file, find the matching ID in the repeater, update those nodes[*]Write a new XML file (replace the old one)Thanks!