How do I benchmark performance of external DNS lookups?

I'm considering Google's public DNS servers as the external DNS for my network. Currently I'm using the DNS servers from my ISP. I've also considered OpenDNS in the past, but ultimately decided not to jump.

I'd like to be able to benchmark how quickly the respective servers are able to serve our DNS requests. I see nothing in nslookup that would help.

How can I test the round-trip times for externally provided DNS?

You can use a packet capture program (filtering for DNS) to track the DNS query\response times. You can run this on your machine or on your internal DNS server (if you have one). All things being more or less equal, this should give you a general idea of how quickly Google DNS is compared to your ISP.

You can just simply dig and grep

$ dig @8.8.8.8   www.rimuhosting.com | grep "Query time:"
;; Query time: 15 msec
$ dig @4.2.2.1   www.rimuhosting.com | grep "Query time:"
;; Query time: 289 msec

Use GRC's Domain Name Speed Benchmark.