Multiple Sites - Multiple F5's - Multiple Exchange Servers

I won't as long as this is for internal-only deployment - in which case the network team has full control over all the paths and traffic. Externally, it might be harder to achieve.

 

The biggest drawback of such deployment in general is that it is not impossible for you to access Exchange through a specific BigIP for troubleshooting or any other purposes. You will also need to have OSPF configured on each BigIP and have it participate in OSPF, as BigIP will have to do route health injection for Exchange virtuals. While certainly possible, this approach complicates overall setup and troubleshooting of live production deployment.