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From what I've read, 1TB drives and even 750GB drives are still not as reliable as 500GB ones. You'd probably be better of buying a firewire 800 hard drive enclosure that can house 2 hard drives. You'll get more space since you can still keep your current internal drive, and you'll have the option to use one of the drives as a Time Machine back up if you so desire. Check out OWC's Mercury Elite Pro.
 
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