OP, i have a question for you. If you're printing this on an inkjet, i'm assuming it's a large format printer, correct? I'm thinking what your trying to achieve is a booth or panel-type output.
If so, at this size you probably won't need to print at greater than 300dpi. Anything above 100dpi will work. Although i could never get the download finished, i'm guessing your files are set at a pretty high resolution.
Memory is not an issue with Photoshop regardless of file size, that's what the scratch disk is for. Once memory is depleted, things do get slower and it will feel like PS has crashed, but it's working. I work on much larger files than this on a daily basis.
If you can upload files to an FTP site for me to take a stab at, i'll be more than happy to help. Just PM if you're interested.
Thanks.