2. Update the planet and keep temp files (`osmupdate --keep-tempfiles`). Apply `osmupdate [-b | -B] --keep-tempfiles` on extract files. This reuses the downloaded diffs and therefore saves time (for downloading) and bandwidth.
3. Use `osmupdate planet.pbf diff.o5c` to generate a combined diff (potentially spanning multiple daily updates) between old and current planet. Apply the .o5c file to the extracts (is this possible?) and to the planet to update these files. The .o5c file should also be usable to update databases with osmosis/osm2pgsql according to http://wiki.openstreetmap.org/wiki/Osmupdate#Assembling_an_OSM_Change_file .
Note concerning variant 3: According to Stefan Keller one possible workflow might be the following: Update the extract using the (unclipped) .o5c file and then use osmconvert/osmosis to _again_ clip the boundary.
