Considering the date they were posted, it seems that it was a last-ditch effort to release SOMETHING before they needed to call these 9.2 drivers. Personally, I think that meant the QA lab didn't have time to test performance gains and kept their testing to stability only. Thus, no performance numbers in the release notes.
That would also explain why the HD 4870 X2 drivers had a seperate release rather than being integrated into the original 9.1 WHQL set. Then again, these are only guesses.

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