Can the USB (v1.0 or 2.0) interface take advantage of more *advanced*
drive
features over the standard 5,400rpm/2MB cache. For example would a newer
7,200rpm/8MB cache be faster at making large back-ups than the older
drives
when they were being used via USB?

Have a look at this FAQ-page: http://www.usb.org/faq/ans2