Both my SuperDrive bays are full (of SuperDrives), so I can't pull power from there unfortunately. I'm really reluctant to go the external power route, as the whole point of this set up has been to have a clean, sleek and powerful Mac Pro without dangling wires.
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Where are you getting your 285 from, and for how much may I ask? I can't find a UK retailer, and importing is going to hit me with huge import taxes/fees (probably in the order of an extra £100, taking the card to over £400!). If it really comes to it down the line I'll bite the bullet and buy one.