Including the 650i Ultra, 650i SLI and 680i SLI, these chipsets support FSB speeds from 1066MHz to 1333MHz, the fastest Intel's CPUs are currently capable of. All of the three chipsets have the built in overclocking capabilities that enthusiasts love, and it's clear that Nvidia wants to directly target the enthusiast market with these. The latter chipset even sports a 3rd PCI-Ex graphics slot. All three support DDR2-800 and have all the stock features you'd expect on a performance line, such as Gigabit ethernet, 4 or more SATA-II connectors and RAID support. The 680i has more than twice the lanes the other boards do, and support having 2 16x cards side by side with an additional 8x card, ideal for a PhysX addition. These new chipsets definitely won't be cheap, reaching up to $300 for the 680i.
The benchmarks pretty much speak for themselves. They outperform Intel's champion chipset, the 975x, to a slight degree, but more or less offer the same performance. Considering the somewhat poor reception nForce initially received as an Intel platform, it's good to see that not only can Nvidia come back with something that performs just as well, but offers a host of new features. The articles are definitely worth a read, and the 600 series is worth considering if you are looking at Core 2.