X38, adding only an improved northbridge and "official" support for FSB-1600 bus speed, though they note that this was technically available in the X38 as well. Tom runs the new entry through a battery of comparisons, so you can get a much clearer idea of what this puppy does. Is this new chipset the answer to overclocker's prayers, or just a waste of an additional $65? Only burning silicon knows for sure.
[Thanks to everyone who sent this in]