There were some rumors that an Android phone would need minimum a 1GHz processor to upgrade to Android 2.3 aka Gingerbread. Google Nexus S gets to launch with Android 2.3 on December, and the Nexus One will be upgraded in a few weeks.
It might be quicker to list the Android phones that might be left out of the Android 2.3 upgrade like the LG Optimus series.That means that owners of the original Motorola DROID live to fight another day. Motorola Droid has a ARM Cortex A8 processor with a maximum clock rate of 600 MHz. If It will get Android 2.3 than many other android devices may get it.