bigdog,
Do a search over on accurate reloading for the .600 OK. This should give you some load data and results. I think Robgunbuilder took the 900 grain bullet to over 2400 fps.

cr500,
You may want to contact American Hunting Rifles at http://www.hunting-rifles.com/ about the brass. It seems they are getting a shipment of brass soon and are taking orders. I did contact them once and they were very nice.