When you're transferring digitally via firewire, it's all just 1's and 0's. Footage of a sunset is just a bunch of 1's and 0's...footage of a football game is just a bunch of 1's and 0's...you get the point.
Being that your video, when digitized via firewire, is just a bunch of 1's and 0's, there's really no way that the quality could differ from firewire port to firewire port. It's all just 1's and 0's, and unless a few of these 1's and 0's get dropped out, the quality's gonna be the same no matter what firewire card you use.
AMD Sempron 2600+ (Socket 754; 1.6GHz)
768MB Crucial PC2100 (I know, I really need PC3200 :()
ATI Radeon 9200