mattbennett1,
That;s a concern as the release notes say files created/modified in V5 are not backwards compatible. That would have to be addressed.
I decided to go with the V5 upgrade, partly because of these potential issues, but mostly because I already own Notion 6, and am not what I would consider a "power user", so Sphere wouldn't gain me much.
I probably should have waited a day or two, but other than what appears to be server overload issues due to a rash of downloads, it went OK. Only real glitch I ran into is it kept failing when trying to download the additional included content items, but it's doing that right now so appears to be resolved - suspect it was an issue with the download server, not the program.
Tim