I have to admit I know nothing about the iTunes download protocol, so I am speaking out of complete ignorance. That said, why would the DNS make any difference? How many name lookups does it do to download what I would assume is one file? Does apple break down large files into lots and lots of little ones? I have used openDNS in the past and it seemed to help a little with webpages that grabbed content from various different place, but I can't imagine why it would help downloading one big file. Of course it could just be my lack of imagination.