The Radeon HD 6000-series of cards is based on the 5000 parts, the only thing different is that the HD 6800 and 6900 cards have been tweaked to deliver improved performance. The 6700 boards, which have the same number of stream processors and the same memory bandwidth as their 5700 predecessors so nothing to see there move on.
It is not as if AMD is trying to con the great unwashed with its marketing move. The Radeon HD 6770 and 6750 won’t be available as retail cards and will only be sold to OEMs.
OEMs should know better, but in case some dodgy sales person tries to convince you that the later series is new and improved you have been warned.
Rebadging is jolly annoying for the consumer, but really good for the manufacturer which looks to be on the ball and producing lots of new chips, when it isn’t. It is a triumph of marketing over substance that they ever get away with it