Handy doc which discibes the performance expectations for migrating mailboxes to O365: http://community.office365.com/cfs-file.ashx/__key/communityserver-components-postattachments/00-00-15-53-58/O365_5F00_Exchange-Online-Migration-Performance-Guide.docx
| Migration tool | Migration method | User throttling | Migration-service throttling | Office 365 resource health-based throttling | Observed average throughput per hour and per client (if applicable) |
| Native O365/Simple Migration | IMAP4 migration |
No |
Yes |
Yes |
5-10 gigabyte (GB) (50 concurrency) |
| Native O365/Simple Migration | Cutover Exchange migration |
No |
Yes |
Yes |
5-10 GB (50 concurrency) |
| Native O365/Simple Migration | Staged Exchange migration |
No |
Yes |
Yes |
5-10 GB (50 concurrency) |
| Native O365 | Hybrid migration |
No |
Yes |
Yes |
10-15 GB (per On-premise Exchange 2010 CAS) |
| Third Party | MAPI |
Yes |
No |
Yes |
0.5-1 GB |
| Third Party | EWS |
No |
Yes |
Yes |
5-10 GB |
| Client Uploading | Outlook |
Yes |
No |
Yes |
0.5 GB |