In Rebex File Server 2017 R1, we added FileServer.Settings.ReceiveBufferSize and SendBufferSize properties that offer more control than UseLargeBuffers. Customers have reported noticable speed increase when setting these to large values such as 4 MB.
In addition to this, we plan to make the File Server's SSH core more efficient and scalable, but this is not part of our roadmap for 2017.
However, even the current version of Rebex File Server is capable of achieving a decent speed and a fair amount of throughput with a decent hardware.
One of our test scenario involved 5 clients simultaneously uploading 600 MB of files files (mostly 2MB - 10MB photos, some videos) over gigabit network to Rebex File Server running on an Intel Xeon CPU with 6 cores (12 virtual cores), 32 GB of RAM and a non-SSD hard drive.
The clients used various hardware (mostly Dell laptops of varying age) and various SFTP clients and took around 30 second to finish the upload. This corresponds to transfer speed of 20 MB per second for each of the 5 clients. The server handled the traffic fine and the total CPU usage was around 7%.
A similar scenario with FTP clients and IIS FTP server (same hardware) revealed that IIS with FTP over SSL is slightly faster (took around 20 seconds).
However, we have not payed close attention to SSH and TLS/SSL settings of various clients, which might have affected the results a lot.