Off-topic, but since you running SBS 2008 I gotta ask:
SBS 2003 does not have a repair option like Server 2003 has. Lets say you corrupted some minor files and the server wont boot. With Server 2003 you pop in the CD and press R to repair it and it copies over all the OS files. SBS 2003 requires a reinstall wiping out your Active Directory thus killing any connection you have with the Exchange 2003 database...unless you have a good backup.
BES 5.0 running on Windows Server 2008 SP2 x64 my calendar would not reconcile. Same install, same AD on Windows Server 2008 SP2 x86 the calendar worked perfectly. This could be coincidence because of something else that changed in my organization at the time but I would suggest against it. Other posters have already noted that BES is unlikely to take advantage of this. If you really want better speed BES 5.0 has HA capabilities which could help in your load balancing.