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I don't think there's a feeling that WinSCP is infalliable, it's just that Martin's not a TCP/IP expert (I don't think, anyway) and I don't think he has any ideas what else he can reasonably do to make WinSCP faster. If you (or anyone who reads this thread) have patches for WinSCP or PuTTY that improve transfer speed, send them to the PuTTY authors or to Martin. I'm sure they'd be happy to see their software made faster.
For me, PuTTY (and by extension, WinSCP) has never compared favorably with other software in terms of throughput. But the user interface of PuTTY and WinSCP is head and shoulders above everything else, so I use them anyway.
[Martin, sorry if I'm putting words in your mouth here.]
Do you know how the performances are different under Windows 2000 and under Windows XP ?
I found on the web that we could improve TCP parameters by enabling RFC1323 options in the windows register.
Have you heard abour this ?
Has someone an other idea ?