When you say 'account' I'm assuming you mean an Inbox account and not an individual mailbox (Inbox refers to mailboxes as namespaces), correct? My concern was data I/O more in the realm of non-text emails (emails with pictures, large attachments, etc.) and while most email providers do have the limit on attachments being 50MB or less it's not uncommon to see that changed in certain environments.
On a semi-related note, what's the typical turn-around time for a request to the Exchange beta? I submitted a request and would love to work on that with you guys but haven't heard back from anyone. I know it's the weekend but just figured I'd ask. Thanks!