Chris
I obviously don't know how Amazon S3 will stand up to large numbers of simultaneous connections but the test I just carried out, while you were posting, showed a worse performance for S3 than your normal server for a UK download. The test was carried out between about 8.30 pm and 9 pm local time on a Friday evening. If it is of any use to you I could retest at a different time of day.
Regards
Nigel
PS a slightly slower download for your legacy files is not a personal concern, as I have either already bought and downloaded all the LL videos or for the earlier LLVJs have the DVDs.