draft-ietf-uri-urn-path-01.txt: performance estimates?

I just finished reviewing the new draft. I like it.

But... it seems that resolution of path URNs would involve failed
DNS lookups, which take a long time, no?

Under "Resolving the URL-sets into the Resource" it says "After
constructin a list of URL-sets, ..." So I get the impression that the,
for example, http transactions don't start until after the DNS
transactions are done. And failed DNS lookups, in my experience, take
15 to 120 minutes.

Are path: implementations expected to exploit parallelism, or is
there some technique for avoiding failed DNS lookups?

In general, do you have any performance data? Estimates?

Dan