another thing to consider.. i think amd also bins thermally.
if a chip is over the TDP at a speed it's stable at, it'll be bumped down to meet the TDP spec.
and then you have to consider that the mobile chips will get the best thermal bins. and the fx should get the highest speed bins that make the 89w limit.

just my theory though

edit: orthoganal. i'd believe that, but that doesn't mean that all wafers are the same