I just did some theoretical math on what kind of performance
requirements I would need to for my virtual machines.

So far my five little virtual machines have maxed out at just under
50,000 KBps (according to the performance charts on the virtual server).
That's approximately 50 MBps of disk i/o. The ReadyNAS 4200 is
supposedly capable of 852 MBps so I should be good there.

A 10Gbps ethernet connection theoretically maxes out at about 1280 MBps.
Not counting overhead I shouldn't come anywhere near the theoretical
limit not even during max performance.

It will be very interesting to see how well running the virtual machines
off of a NAS unit filled with SATA drives over a 10 GBps ethernet
connection will work.