How about some mathing!
So...if 1 minute of 44.1 16 bit takes approximately 10 megs of space...
88.2 16 bit is 20/minute, and 96/16 is 22, then 96/24 is 33MB/min per track.
If firewire 400Mega-bits has a theoretical throughput of 400 * .8, 32 megs a second. Then not counting overhead, you have the capability of almost 60 tracks. But lets assume about 25% loss to overhead, so that leaves you with 45 tracks on a firewire 400 device at 96/24. Seems pretty reasonable huh...
So...go with the device that is the most practical for you. If your DAW doesn't move, then don't waste the extra money on the fire, but if you might have plans to use a mobile computer, or perhaps even record to another system, go with fire!
Jake