I definitely don't claim to be an expert in Exchange by any means so here are my few simple questions:
Can you increase the max size of users' mailboxes to larger than 50GB?
Does doing so circumvent the 50GB max file size limit of Outlook?
Does allowing access to different mailboxes combine the file size on the local machine?
for example: if John accesses his own 25GB mailbox and also has access to Jill's 25GB mailbox in his outlook, does that combine and reach the 50GB outlook limit?
I think that's mostly it for now.