If I understand correctly, these are addressing two different issues. Namebench seems to be interested in finding out which DNS server will return a look up request the fastest. The OP though is saying that because global DNS providers don't currently pass along information about my local IP address, I'll get a suboptimal response that points to an IP address that may not be the fastest for me.

Or does namebench actually test the IP addresses you get in response to test their response time?