Thanks very much for the link, that's some interesting in-depth reading.
http://www.all-things-photography.co...print-pro.html might help if you're still going for the 50mb file size, but personaly i find it far easier to meet the 4mp requirements of most microstock sites. Normaly they're happy for you to submit in jpg provided it's at minimum compression (ie- no compression artifacts) which can save a lot of upload time.