How to maximize SFTP upload speed?

I support an office of about 75 users running network traffic on 100Mb/Full duplex internet switches. My problem exists with one user in particular. The past support crew made some configuration changes to this user's Lenovo desktop PC running Windows XP Pro. The WinSCP version on this machine is 4.1.9. This version is transferring files via SFTP to an external SFTP server at a different business. The upload speed on this particular desktop is roughly 500-800kb/s. Every other machine running these same uploads only transfer at approx 100kb/s.

My question is, after matching the NIC and WinSCP configurations EXACTLY on all other machines, what could have been done to the PC in question to make it upload so much faster? Something at the server level or desktop level?

1. Eliminate the network from the consideration:
Move the network connection to another PC configured to what you think is identical.

If it follows the network, its either network setting on the switch, or the server side.

If it follows the PC, then its something on the PC.


2. check tunable network parameters. For the PC, something would've had to be installed to allow you to tune those. This is relatively uncommon though.