Nice and interesting reply. It certainly gives a lot of insight on what is happening behind the scenes.
Anyway, I really believe ATi should explore the possibility of pushing for legal action against HA.
After all, we are talking about slander/libel here if the benchmarks do not correctly reflect the quality of R520 hardware. In most cases, the most difficult point to prove would be the malicious intent, but this is not a problem here since this has been established on HA's website, not to mention that ATI could easily produce the emails in court.
The next point to establish the damage suffered as a result of the publication of this "preview". This shouldn't be too difficult to prove either : the article has been read by millions of people and has been mentionned on most hardware sites, thus affecting the trust and confidence of your consumers and investors.
The only point left to prove is that the article is wrong and misleading. This should be very easy to prove. If HA really made up these benchmarks for the sole purpose of bringing down ATi's stock price, as this was clearly pointed out in the emails, ATi should not let HA get away with it so easily.
ATi would have nothing to loose. HA would on the other hand, and nothing in that article would protect them from having ATI make an example from them. His 'disclaimer' is not enough to protect him either. Even iIf you have some kind of disclaimer like, "I don't know if this is true and accurate, but bla bla bla" it still doesn't protect you from getting sued, unless you can show that others believe so.
In the words of Lord Devlin (UK) in Lewis v. Daily Telegraph Ltd., [1963] : One cannot escape liability for defamation by putting the libel behind a prefix such as "I have been told that ..." or "It is rumoured that ...", and then asserting that it was true that one had been told or that it was in fact being rumoured.... For the purpose of the law of libel, the hearsay statement is the same as a direct statement.
Anyway, my advice would be this : I believe you should seriously consider pushing for legal actions, or even a settlement. You have nothing to loose, and all to gain.