The Quantum 600A shows the most promise for building a searchable tape archive from MXF files, since they support that data format natively.
I can say that I have been using bluray in both 25GB and 50GB capacities for a few months now, and it works out well.
See my blog if you are interested in more details about it...-
Art Aldrich
Leader, NJ FCP UG
http://www.njfcpug.org