You probably know this, but those BB7 brakes weigh a ton...

This might be one case where building a rear wheel on a tandem axle would make sense. The 145mm, doesn't do that much for spoking angles but it does allow some extra space and to not have a dished rear wheel while running disc brakes. DT is one option, and probably phil and others. Shimano doesn't have a hardened axle, possibly because it isn't all that necesarry but it is a nice to have, I have seen bent axles. Plain bearings as in the DT are a nice feature cassette bearings are not as free turning, massive, and how do you go ceramic? Personally I am going with Phil. XT with hardened axles is a nice cheap option.