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Try benchmarking the DNS servers with something like Domain Name Speed Benchmark. Or just try Google Public DNS.
To really see results, the easiest way is to use a program the was developed by the good people at Northwestern University called namehelp. You can download it from the University website, and there are versions available for Mac, Window, and Linux. From the website:
"namehelp improves web performance by obtaining more accurate redirections to nearby content delivery network servers.
Basically, namehelp improves your web performance when either you or your ISP uses a remote DNS service."