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While it should work and simply downclock to 667MHz according to JEDEC, some reports of people trying it got a non working machine with the 800MHz.

Haven't seen if people have had more luck lately, with RAM that works in the iMac.

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Sort of really is a non-issue since the MacBooks skipped directly to DDR3 anyhow so it isn't like you will keep them for the next machine.
 
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