If the 6870 has the punch (or greater than) of the GTX 480, that would be swell. But it also needs to remain in a conservative power envelope and an acoustical one too. The two reasons i didnt buy Fermi (three sorry) were: Power/Noise and Delays.
If the 6xxx series keep the power and noise down then it's very very bad news for NV. Furthermore, if NV have no answer to it (unknown at this point) developers will more likely look more and more to ATI for 'affiliation'.
Which could be very bad for prices.......