Wonderful image Mike. I just used a plug in from Genuine Fractals
http://www.ononesoftware.com/detail.php?prodLine_id=2
to enlarge the image to 4000x13000 pixels and saving it in PS at max quality (12) gave a file of size 10,520KB. Using the usual bicubic algorithm gave a file size of 8,317KB again at max quality.
I think it does a much better job of producing larger images for printing posters say. There is a free trial version.Below are a couple of crops from each.
Bert