For archiving? On write-once media? Looking at Wikipedia and associated pages, I'd say there is effectively nothing changed.
Each new UDF version builds on the previous version unless otherwise specified. So 2.60 can, for example, support the metadata partition that was brought about in 2.50, and there wouldn't be a major change.
However, since 2.60 brought about that "pseudo overwrite partition", which from the way it sounds is a way for you to update the disc at a later time on discs where you can't literally rewrite the media, 2.50 wouldn't support that. But again, that's only for appending data that would "overwrite" old data -- say updating a document to a new version might use this.
But you could still do multiple disc sessions and "update" files in previous versions. This is just a new, potentially more efficient way of doing things.
The metadata partition thing is apparently supposed to increase performance (putting all the extra file details in one block, I imagine, is more efficient that scattering that information out next to each file on the disc). Depending on the program/implementation, the part of the software that creates the file structure &etc may duplicate this information, meaning the metadata won't be lost. But that doesn't mirror the entire contents of the file.
Basically, if you're really going to be archiving using a standard archival tool, the chosen file system will not matter too much. If you're merely going to be burning things as standard data discs (which I suppose can count as archival, though not the best option available), then maybe UDF 2.50 would help. MAYBE. But in general, you don't run into an issue where the drive can't tell that files are there; you really run into issues getting the contents of a file back, if not getting the contents of the entire disc back. Avoiding that kind of problem goes beyond the scope of the features added in new versions of UDF.