IgorsLAB posted a review on the AMDs Pitcairn with 768 SPs in
A quote from the article:
Why do you think there was no HD 7830, but the rather unloved HD 7790? We had reported in a news item back then that we came across a board during the test of a new Radeon HD 7850 in the rare singleslot design, which didnt contain a normal Pitcairn chip with 1024 shader units.AMDs Pitcairn with 768 SPs in review