For doing (synchronous) volume replication, you're going to need a REALLY fast VPN. The inexpensive one we can find won't go much faster than a T1 (which is fine, since that's the only connection we'll need), but we use (asynchronous) data replication (i.e. file-level replication), so 1.5 Megabits/sec is fine for us.
I am thinking you would need a VERY fast VPN to get 40Megabytes/sec (i.e. 320 Megabits/sec), which is the default bandwidth set aside for volume replication.