I doubt very
much each and every card is tested for it's OC ability. They will just be tested to make sure they're functioning properly. That would explain how there are a crap load of over heating 280's about. They will have been tested and passed but not run for 30 mins on full load. Can you imagine how much that would cost a company to do. (EDIT: Probably not as much as all the RMA's
What I do think will be true is that many, if not most, 260 chips will be 280 chips with a failed cluster (correct terminology?) of cores. If fact I would say the 280 range would not have been viable without selling some of the failed GPUs as 260's. nVIDIA will just be trying to claw some of the money lost by low yields. Like Intel did with P4's and Celerons, etc.