pcmcia vs. firewire

As common as it is to find eSATA storage devices, what benefits are offered over firewire? I understand the cable transfer rate is better, but when the internal transfer rate of a hard drive is unchanged and is below that of the cable transfer rate, what is the point of upgrading. Also, what are the cpu demands of both? If I were to go with an eSATA I would have to add a pcmcia card to my laptop to provide a esata port. I was interested in finding out if the transfer rate of the pcmcia card is slower than firewire. Will the eSATA be bottlenecked at the pcmcia interface? Thanks.