The Core i7 900 series codenamed 'Bloomfield', consists of the original Core i7s which are used in LGA 1366 socket motherboards, they use triple channel memory, up to 24GB and the X58 chipset which is the only chipset available for LGA 1366, provides two PCI-e 16x lanes.
The Core i7 800 series codenamed 'Lynnfield', which are newer, released in 2009 IIRC, and have a lower TDP of 95W compared to 130W, and have a higher Turbo Boost. The Core i7 800 series only support dual channel memory, up to 16GB, and is used in LGA 1156 motherboards which are normally based on the P55 chipset which provides one PCI-e 16x lane.
General Summary: Core i7 860|Core i7 930
Stock speed: 2.8GHz|2.8GHz
Max Turbo Boost: 665MHz|266MHz
Max stock speed w/Turbo Boost: 3.46GHz|3.06GHz
Socket: LGA 1156|LGA 1366
Memory channels: Dual|Triple
Max. possible memory installed: 16GB|24GB
Main chipset: P55|X58
PCI-e lanes available for graphic cards on respective chipsets: 16|32
i7 970 is due 3rd quarter this year and it won't be an Extreme Edition. Doesn't mean to say it'll be affordable though - there's been suggestions and rumours that it will only be about a hundred bucks cheaper than the 980X.
We'll have to see when it comes out.
Yes, the X58 platform is the most powerful you can get on the desktop but a lot of the time the price premium that goes with it doesn't always make it the best choice.