Often I hear people claiming S3 is slow, when in fact S3 is very fast but the user space program you are using is slow!
This gist provides a tool: rapid_s3_upload.sh
which will upload the directory you run the tool in to a provided S3 bucket, as fast as humanly possible.
This tool will saturate your NICs, will saturate your CPUS, and will upload data to S3 faster than basically anything else.
rapid_s3_upload.sh s3://some-path/in-s3