I know it's a little low tech but FWIW I'm currently just using:
rsync -avzH --delete \
--exclude=sites/Fermi --exclude=archive/debuginfo \
--exclude=archive/obsolete \
--include='/5[2-9x]/x86_64' \
--exclude='/*/*' \
rsync://rsync.scientificlinux.org/scientific/ scientific/
to grab just the x86_64 distros.
Works for me...
John