Transmit is every bit as fast as Yummy downloading and uploading a 10Mb file (S3 and SFTP), so I'm not sure what your impression is based on.
The last release was 11/24/08. It's always updated to take advantage of/fix bugs introduced by new OSes. There hasn't been a release in a whopping 5 months (?) because Leopard's been out for a while and there aren't any outstanding bugs.
Yummy FTP ist the fastest and feature-richest FTP-client for the Mac. It’s synchronization feature is really good. (I bought both)