Furnish new ball-park benchmark numbers

I now think I understand why the 10MB (actually 13MB, amended to be
more accurate) file test was *so* slow, although it did not occur to
me at the time: S3-Classic/US-Standard may opt to home keys across the
continent from one's instance, and this does not seem to converge over
time (e.g. through mirroring).  So, this can be re-cast as a "slow
link" test.  It seems this can happen if one uploads to S3 from a
place geographically closer to Seattle, unless one uses the
s3-external-1 endpoint.  I uploaded the test file from such a
location.

So, I uploaded the file again from AWS us-east and re-took the
measurements, now affixed.

I tried another small key made from within EC2 us-east.  This has
become a new benchmark for "the very fast and very small" case, where
special code is triggered to avoid multi-request parallelism.

Most mysterious is Amazon CloudFront: I cannot get it to perform well
with htcat at all, although it's offering excellent curl performance.
It's not even abundantly clear that slower processing of Range
requests is the whole story: I'm still baffled by the stark nature of
the results and a few other bizarre observations.