Using a directory of mixed files (jpgs, tiffs, RAWs, other), I get these benchmarks:

ls -1 | xargs -n1 exiftool -S -a -e -G1

~ 35 seconds

ls -1 | xargs -n100 exiftool -S -a -e -G1

~ 13 seconds

Calling exiftool once per file is 2-3 times slower than passing a list of 100 files. So the initialization overhead is pretty severe.

-Mike