8k5a2+ advice

Hi all,

I'm still using my old trusty 8k5a2+ I would like to add a 1394b
(firewire 800) card to it to run an external hard drive.

My question is will it run at the full speed, or only run at the old
firewire speed, I heard that some older motherboards won't be able to
run at the higher speed, because of the pci bus/slot won't let it?

Any help would be great!

Many thanks

Matt