firewire 800

Hi, im curious as to why you would need a 9 pin to 9 pin cable to work with a firewire 800 adapter card if you already have a 9pin to 4pin and a 9pin to 6 pin that will connect to almost any desktop and laptop ? I remembered last year you didnt have any option but to get the firewire 800 adapter card because 9pin to 9pin was the only cable available but now you with the other 9pin to 4 or 6 pin cable i dont see why you would need one..Is there any advantage from using a 9 pin to 9 pin over a 9pin to 4 or 6 pin fireiwre 800 cable ?

another question is if i plug in a firewire 800 9 pin to 6 pin cable onto a pc that has a FW400 6 pin port will i only get firewire 400 transfer speeds instead of firewire 800 speeds ? Do you only get firewire 800 speeds on a 9 pin to 9 pin cable ?