FUD Zilla noticed it may be possible to turn a Radeon HD 6850 into a Radeon HD 6870 by upgrading the BIOS and overclocking the card:
Some of the review sites have received some quite interesting Radeon HD 6850 samples, those that have all the 1120 shaders enabled. According to the posts, it is simply a matter of different BIOS and HD 6850 could end up with 1120 instead of the 960 Stream Processors.
Of course, this might end up to be just a few isolated cases in the beginning but hopefully users will be able to flash the BIOS and make such cards. Both the Techpowerup.com and Computerbase.de ended up with such a card. It would be interesting to see if any of those card actually ended up on the market and if some of the early adopters were lucky enough.