I think this will depend more on the internal router architecture than on whether the access list is named or numbered. For example, some routers and switches can handle compiled access lists in hardware.
There are some small differences in functional behaviour. the new feature of numbering the lines of an access-list so that you can insert lines in the middle - that only works with named lists. OTOH, ip accounting access-violations only works with numbered access lists, and not with named ones.
Kevin Dorrell
Luxembourg