Hi everyone. Thank you for your responses so far.
As several of you mentioned, stock buyers make their decisions on small thumbnails, so any qualitative advantages of MF won't be visible. However, the available file sizes are visible to the buyer. So the question I've been asking myself, and which I posed in this thread, is whether having the larger file sizes gives one photograph an advantage over others, all else being equal. Obviously buyers make their decision on content first and foremost, but once they narrow their selection down to a few equally acceptable photos, I'm wondering whether the larger available file size will end up being a deciding factor. In a highly competitive environment, every advantage helps.
Regarding charging more for bigger file sizes, I was indeed referring to Alamy's royalty free license model. I guess I should use their cost calculator on their rights managed files to see if file size comes into play, but I don't recall seeing file size as one of the variables the last time I looked.
One thing I didn't mention initially is that my main focus is (or will be soon) fine art landscapes sold thru galleries and direct web sales. I view stock sales as a supplemental source of income. My main interest in MF is to get the highest quality files possible (and still shoot digital) for the fine art landscapes. But that got me to thinking about whether MF files also conferred some advantage in stock sales. So that's why I posed my question.
Thanks,
Hans