This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Liquid Technologies offer a large file editor in their product, its not free but it is available for a 30 day trial, so that should be plenty to accomplish what you have in mind. Their website claims it can open GB and TB files so again 6MB shouldnt be a prioblem. I havent used the feature myself so please do feedback if it works or not. More info here; http://www.liquid-technologies.com/Large-File-Editor.aspx
Notepad++ is free; I haven't found a file it can't open and 6 MB is certainly within its range. It offers syntax highlighting, collapse/expand tags for a variety of "languages" including xml.
Everything is theoretically impossible, until it is done. ~Robert A. Heinlein
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com