Format preference for incoming mail: Keep in senders' format

Recently we are getting a rash of people who are getting 123.DAT 
attachments.  I don't know why they are not starting to flood me with 
requests to fix this but I know how to fix them one by one.

Is there any reason NOT to globally change all users that have:
Format preference for incoming mail:    Prefers Notes Rich Text
to
Format preference for incoming mail:    Keep in senders' format

The help says:
If the user is an IMAP or POP3 only user, selecting Prefers MIME provides 
the best fidelity and performance.
If all clients and servers are V5 or later, selecting Keep in senders’ 
format provides the best fidelity and performance.
If the environment includes V4 or earlier versions of the product, Prefers 
Notes Rich Text provides the best fidelity and performance.

We started out on V4 but there isn't a hint of it left anywhere in this 
domain.  Just holdovers you suspect?

I am thinking about requesting my manager to have our Notes security 
person just change everyone that has the one to the other.

Rob Berendt