"svn diff -r <some_rev> file1 file2 ..." with several dozens of files
(where the filenames are typically obtained by using a wildcard) is
much slower than just "svn diff -r <some_rev>"; it is so slow that it
is rather unusable. It seems that svn takes the files individually
instead of globally.

This happens even when most of the files have not been modified
since <some_rev> (the Last Changed Rev is available locally).