We've learned that if you combine the top Asus X58 motherboard, put some overclocking effort into it and use some of the upcoming DDR3 triple channel memory, you should end up with up to DDR3 2000 speeds.
Companies such as Corsair are currently investigating Nehalem's top memory speed and it looks like they should be able to launch DDR3 1866MHz in triple channel kits. Some modules will run at DDR3 2000 but we believe that Corsair will initially launch DDR3 1866 and go for higher speeds later.
As Intel officially certified DDR3 1066 only, this will be pure overclocking, but at least it will give you some decent memory speed. Triple channel fast DDR3 memory from Corsair and other memory partners will launch with Nehalem, so you can expect it in November time.