The MS Press, SQL Server 2005 Implementation and Maintenance book (pg 637) indicates that High Performance operating mode of a database mirror can have "greater geographic separation between the principal and the mirror" because the transaction transfers are asynchronous. The High Availability mode requires the transaction be confirmed on both the primary and the mirror before it will send a commit confirmation to the application.

My question is, what level of a performance hit would a High Availability mode mirror with principal on the east coast and mirror on the west cost have ?