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.