Harpertown the soon to come FSB 1600 server chip and Yorkfield quad core are the same chip. Its mother is the same wafer and it is all about the packaging.
Intel folks claimed that there's optimization on the Harpertown to make it a better server boy, but I
guess this is all up to bios on the board.
The biggest difference is the socket as Socket 771 is for servers and socket 775 is the one we will use for desktops even in the future.
This means that Yorkfield gets official support for the mighty FSB1600.