Interestingly, when Intel started using the "Extreme" moniker in the late days of the Pentium 4, the only real difference was that the Extreme chip had twice as large of a cache. The Core 2 Extreme chip, however, has the same cache size as the non-extreme version. There are still some differences, as was pointed out already, but it started out as a marketing gimmick, and now it's even more of one.