Nvidia's new Fermi cards haven't been runaway successes, but the GeForce GTX 460 has managed to hit the price/performance sweet spot. However, it looks like AMD will have an answer for it -- apparently as soon as next week.
The new Radeon HD 6850 and 6870 are rumored to launch on October 22, though there's been no official confirmation or pricing details announced yet. There's a bit of confusion around the naming of these cards, as they will actually replace the Radeon 5700 series and not the 5800 one. As a result, these should not necessarily perform as well as the 5850 and 5870, but an early benchmark leaked on Chinese Web site XFastest show that they provide a major boost over the 5750 and 5770.
The 3D Mark scores indicate that the 6870 (P16270 in 3DMark Vantage/19480 in 3DMark06) does indeed top the 5850 but it's still behind the 5870. However, both new cards beat the GeForce GTX 460 and obliterate the GTS 450. We'll have to wait until benchmarkers get their hands on the cards before we know how well they compare in actual gaming benchmarks.
As always, pricing will be crucial to the perceived value of these new boards. Performance that tops GeForce GTX 460 at the price of the 5700 series will be tough for Nvidia to beat. Lest you think AMD has forgotten the high-performance market segment, there should be a Radeon HD 6890 on the way, as well as the 6900 series, which is the true replacement for the 5800 lineup.