2 cards are hashing alot lower than use to

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have 2 280x one xfx black edition and the other asus dcu2t. and they are hashing vtc at 257kh/s while before they used to hash at 350kh/s? Restarted the pc no effect. I also have 3 other xfx black edition connected to the same rig hashing at 350kh/s.