A Microsoft tool, LoadSim, simulates large numbers of Outlook™ clients performing a range of typical client operations. Naturally, due to the server's compatibility, it also works against the PostPath Server™.
Using LoadSim in PostPath's labs, we have measured the PostPath Server performing five times (5x) as many transactions per second as Exchange on the same hardware. The PostPath Server performance also degrades much less as mailboxes get large.
This level of performance advantage is what enables use of much lower cost storage; the use (combined with easy backup and restore at the server) of large mailboxes instead of user PST files; and server consolidation.