Thanks, smaffulli! That worked very well. I executed the commands you gave. One note: The output for each of these commands is different, 's3cmd ls --list-md5' places the md5 signatures in column 3, or rather,
array[timestamp, size, md5, s3://bucket/object]
and your find command puts the md5 signature in column 1, followed by the path of each file.
Someone with better knowledge of shell scripting may know how to quickly compare the md5s in each; I pulled them both into OpenOffice Calc, took out the columns I didn't need, sorted them, and then, after consulting this thread on StackExchange,
was able to confirm that one of my buckets is absolutely the same as the local folder. For now that is fine, and I know where to look if I want to do a complete test.