curl -s http://public-dns.info/nameserver/pl.csv > list; cat list | cut -d "," -f1 | \
xargs -i timeout 1 ping -c1 -w 1 {} | grep time | \
sed -u "s/.* from \([^:]*\).*time=\([^ ]*\).*/\2\t\1/g" | grep -v "1 packets" | sort -n

Więcej informacji: DNS servers in Poland