edtFTPnet is actually pretty fast - although .NET being a virtual machine it is unlikely to be as fast as a natively compiled FTP program.
You could experiment with a few settings - put the TransferNotifyInterval property to something very high, e.g. 1 million. Set the TransferBufferSize to say 32000 or 64000.
You've also got the source so if you want to look into it a bit further, try to pinpoint where you think it might be slow. If you can, we'll take a look and fix. We haven't looked at speed for a while so we'll do so again anyway.