techies correct me if i'm wrong here
Respectfully, there is some incorrect information here.
First, with regard to speeds, Firewire 400 is not terribly quick by today's standards. It's max data transfer is 400 Mbits
/sec, which is just under 50 MB/sec. Note the units change there... bits vs Bytes. Roughly 8 bits per byte. Firewire is defined in Mbits/sec, while most modern devices specify data transfer in megabytes per second (MB/sec).
So, is 50 MB/sec "fast enough"? It depends what you are doing, I guess. However, modern hard drives can easily exceed that transfer rate, both peak and sustained transfers. If you are using a recent hard drive on a FW400 bus, you are probably limiting the transfer rate. That may or may not be a problem.
For example, I use external RAID0 arrays on FW800 for Pro Tools, and I can test the drives at 80-90 MB/sec sustained transfer with no problem. Do I need that bandwidth? Yes. Depending on the number of tracks, the sessions sometimes reach the transfer limit when connected via FW400.
Second, you can mix devices of different speeds on a FW800 bus. As long as the maximum limit of the bus is not exceeded (just under 100 MB/sec), each device is independent. Connecting a FW400 device does not slow down a FW800 port. That's part of the design specification.
That's completely the opposite of USB2.0, by the way, which may be where the confusion comes from. A USB2.0 port is limited in speed by the slowest device on the chain. They fixed that in the USB3.0 specification (which is closer to Firewire in basic design).
You need to be smart about physically connecting devices, however. If you have a FW800 port, the FW800 devices all need to be connected directly to it via the larger connector. The FW400 devices need to be at the end. This, for example, will not work:
Well, it will work, but both drives will be at FW400 speeds. Do this, and both drives will be at their maximum transfer speed:
So why don't more computer manufacturers put in FW800 ports instead? I think it requires a higher licensing fee, and I also think the parts are slightly more expensive. Apple can do it because they are one of the original Firewire patent holders, but everybody else needs to pay a licensing fee to include a Firewire port.
If you want a FW800 port, I recommend Unibrain products: Welcome to Unibrain web site - The Firewire (Firewire 800 - IEEE 1394b) Innovators
Their newest PCI and PCIe cards are very good: FireBoard 800-e™ 1394b (Firewire-800) OHCI PCI Express adapter FireBoard-800™ V.2 1394b (Firewire-800) OHCI PCI adapter
And yes, a standard 32-bit PCI slot is enough for FW800. Unless you have other high-bandwidth PCI cards in your system (RAID controllers, for example), the PCI bandwidth of 133MB/sec will be sufficient to supply a FW800 card.