BUS Speed Question

Before I go digging into the depths of google I was wondering if anyone has the answer to this question in regards to bus speed. I'll tell you what I am planning.
At the moment we currently have a media server which is a shuttle P4 Desktop with plenty of Ram and diskspace etc. Hanging off the back of that on a firewire 2 port is a LACIE 500GB external hard drive. This is what holds the media files etc. Now this is almost full & I want to increase the size. At the moment I back this up to 2 other [ one on site and one off site ] IP Lacie Hard drives.
Instead of splashing out on a terabyte or 2 terabyte external hard drives I want to go down the Freenas route. [ www.freenas.org ]
I have already have a FreeNAS box just to hold and deploy our ghost images and this works well. I have two 160 gig mirrored [ software ] HDs in an old Dell box.
Now in the latest beta ver of Freenas they have introduced JBOD so you can join two disks to make one large volume. [ I have tested this already with two old 20 gig drives without a problem ] This is my plan, two 750 gig drives. So around 1.5 terabytes. I will do the same on a different Freenas box and use the RSYNC function to back it up.
Now on with my questions in regards to bus speed, I know the JBOD won't help but am I correct in stating if I house the two 750 gig drives on the same PATA / SATA interface, this should operate faster than the firewire 2 connection ? Does anyone know the bus speeds for PATA / SATA against firewire 2 and also will having the two drives on the same interface make the JBOD quicker or won't that make much difference ?
I have my test box on this ready to test later in the week but would appreciate some knowledge on the different bus speeds. The NAS boxes will also be networking on 100 meg ethernet cards but I may go down the gigabit route if required... [ Although I don't think would make much difference as the other buildings only have 100 meg switches, the gigabit switch is looking after the ICT suite & servers.

Looking at it logically, the disk(s) in the external drives will be connected on some kind of PATA/SATA controller so there really won't be much difference in speed there. However, the interface between the PC's firewire connection and the external drives is bound to introduce an amount of latency.

If you are really bothered about high speed disc access you should be looking at a SAS-based SAN but that will probably be out of your price range ;)

I would say the 100mbit nework connection will be your main bottleneck.

Andrew