According to this article originally posted on a German website, AMD is producing such good yields on Athlon 64, that it's considering not releasing any clock speeds lower than 2GHz when it launches next month.

Additionally, The Inq has posted some rumoured model names and PR ratings for Athlon 64 processors depending on the platform they will run:

The article says AMD will introduce an Athlon 64 FX-55 at 2.4GHz (940) pins, an FX-53 2.2GHz (940) pins, a 3700+ (2.4GHz 754 pins) and a 3400+ (2.2GHz, 754), but the higher speeds probably won't appear until next year.

If this information remains true, it would mean that the 'FX' nomenclature would end up going to the high-end parts of the family and not become the new Durons, we will have to wait until final announcement.