Why don't u try the external sata 2. That must be faster the Firewire 800 , High-performance storage data transfer up to 3.0Gbps (300MB/sec). And the SATA2 hd is very cheap nowaday.
This is the cheap option:
PPA Int'l 1165 SATA II ExpressCard 54 - OEM
http://www.newegg.com/Product/Produc...2E16839228001R
DCS1-1205 Bridgeboard external power supply
http://fwdepot.com/thestore/product_...roducts_id/604
ANd the cashy option would be perfect, because
SeriTek/2ENSM2-E bundle ExpressCard Adapter and External Enclosure
http://fwdepot.com/thestore/product_...oducts_id/1575
or
http://search.ebay.com/sata-raid-enc...sPageNameZWLRS
and the card