Need help with G5 1.8 single - firewire400 - FCP 4.5

So here goes. I am running FCP 4.5 on a late 2004 G5 with a 1.8 single processor and 768MB ram, and OSX 10.3.9. I am using a Firewire 400 for media storage. I realize my system is out of date, but I've never had a problem with it until recently. I am starting work on a trailer for a documentary shot on a Canon XL2 in 24p normal. (Previously I edited stuff shot on a Sony handicam, so this is much higher quality footage than what I'm used to.) I have what I need captured and ready to edit, but Final Cut is incredibly slow and unresponsive. I suspect it is the firewire 400 that is slowing things down, but before I go out to spend money, any other suggestions for speeding up my system? Is it better to go for an external firewire 800 or a serial ata drive? Will increasing my ram help at all? Thanks in advance for your help!

in THIS case, more ram will probably help.

firewire400 is FINE. unless its just a crappy drive - and that does happen sometimes. what kind is it? im gonna guess lacie or western digital... i was using firewire400 exclusively until about 2006 and it never let me down.

how full is your firewire drive? drive performance DOES drop the more it fills up.

firewire800 and eSATA will both be better , but dose youre machine have an 800 port? and eSATA will require getting a PCI sata card.

start with the easiest first. get about a total 2 gigs of ram.

Yes, my firewire is a lacie, and my machine does have an 800 port, but I'll go for the ram upgrade first. My firewire is only using 60 of 150 gigs, so I don't think that would be the problem. Thanks for the help!