If you can spare a 1 gigabit connection to saturate with S3 uploads, you can send 50TB in about two weeks. It takes about a week to request a Snowball, have it arrive, you fill it (takes about a day, assuming you have a 10Gbit connection for Snowball), you ship it back, they copy the contents to AWS storage. If you don't have a spare 1 gigabit connection, the speed is that much better. Even if you don't have 10Gbit hardware to fill Snowball with, a local, dedicated 1 gigabit connection to Snowball would be much more reliable.