I’m not going to offer much advice on the server side of it, other than to state my overall preference for HP server hardware using Opteron processors when doing virtualization. Any of those 3 systems you’ve listed would work fairly well for you, just go for the one that you feel the most comfortable with and offers you the most bang for the buck. Where I will offer a specific recommendation is on the storage side of the equation. If you can find a dealer that you can get service and support for it, look at Scale Computing and their HPC clustered storage solution. They make a system that is easily expandable, very affordable, simple to configure, and very high availability. For about $13k US, you can build a 3TB iSCSI SAN, or configure it as a NFS NAS. The data throughput is excellent, and expanding storage on the system is as simple as plugging a new unit into the array. For the money, you won’t find another storage solution out there that offers the level of redundancy and amount of storage that Scale does. Check them out at http://www.scalecomputing.com
Good luck with your project. My $.02 worth.