I have a customer (tech, not graphic) who has a 2GB map in an ECW file. IrfanView is said to open the extension, but throws an error. We tried a 600MB file and the same error.
It's a one off job, so I'm thinking it may be easier to find different software rather than troubleshoot the error, which doesn't give any info on what the error is related to.

Does anyone have any experience with this extension and such a large file?

The file is a detailed map of Australia from the Aus governments website if anybody is curious.