This question is not just strictly about the spec, it's also about what the most common readers will accept.
So the file offsets are 10-digit numbers, is the maximum safe offset 2,147,483647 or 4,294,967,296 or 9,999,999,999?
I understand about "large" files and older OSs and so on, and I don't care about ancient lame OSs with 32-bit max file sizes...