I'd like to say a couple of things:
-
RAID 0 scares me a little: any problem with one HD and everything is gone, and i'm not talking hardware failure of a disk, but say a quirk of the controller chip, wich is rare but can happen;
-the stock cooler of the HD4850 is not effective, i'd go for aftermarket solutions, expecially since you are going for a dual configuration.