The last couple of overclocked CPU I've bought weren't pretested. I just go by luck of the draw. I've bought two 500E aC2s. One was able to hit 700 @ 1.7V, the other 750 @ 1.8V. I just recently bought two 650 cB0s. One goes to 911MHz @ 1.8V, and the one I'm using now is running at 1021MHz @ 1.8V.
It's more fun and costs less to overclock without a guranteed speed. But thats just my opinion.