ok i just performed some more tests and you guys are 
right, the GET responses during update mode were all 
304 except for robots.txt, which is expected i guess. 
also, total incoming data in update mode was 
significantly less than mirror mode (3k vs. 42k).

the site where i saw almost identical download times 
for mirror vs. update modes was 
<http://www.oldskool.org/pc/help/oldonnew/>, which as it 
turned out consisted mostly of .shtml files. NOTE: a 
file comparison between a redownloaded file 
(01_intro.shtml) and the original revealed _no_ 
differences in the files. does this mean that 
all .shtml files are forced to be redownloaded every 
time even if they are apparently static?
thanks,
tom