I don't know of any portable storage devices that use Firewire and some have internal drives that are just 5400 rpm as this (supposedly) makes them more robust. Most modern units do use USB2, which isn't that slow.
As for fast card to computer transfer, you want the latest UDMA reader such as the new Lexar Professional FW 800 UDMA CF Reader, but you will need to invest in the fastest CF cards to get the benefit. There are two factors: connection speed (Firewire 800 being the fastest) and the actual read/write speed of the card.
Identify what your bottleneck is and go from these. There's no point buying UDMA cards without the reader or vice versa and you will probably need to add firewire 800 to your computer - Firewire 400 is the norm. It's a different connector.
As a workaround, you could get some extra cards and download when you're back at base rather than trying to do it in the field.
What are you using at the moment?