What is the most efficient way to move a large number of files that reside in a single directory?

Taking advantage of GNU mv's -t option to specify the target directory, instead of relying on the last argument:

find . -name "*" -maxdepth 1 -exec mv -t /home/foo2/bulk2 {} +

If you were on a system without the option, you could use an intermediate shell to get the arguments in the right order (find … -exec … + doesn't support putting extra arguments after the list of files).

find . -name "*" -maxdepth 1 -exec sh -c 'mv "[email protected]" "$0"' /home/foo2/bulk2 {} +

Consider mving the parent directory instead of the files:

mv /home/foo/bulk /home/foo2/bulk2 && mkdir /home/foo/bulk

(But it might cause problems if /home/foo/bulk must exist at every moment.)