Upload speed only less then half of the bandwith used

Hi!

When I upload files with WinSCP only half of the bandwith is used for the actual upload.
The Windows network meter shows 5 MBit/s traffic used by WinSCP (this is also what I pay for to my ISP) but WinSCP transfers only about 220KiB/s. It should be over 500KiB/s if you do the math!
The command line version of Cygwin/SCP reaches around 600KiB/s connecting to the same server with the same file so it could not be a protocol overhead.
What is going wrong here?

I tried SFTP and SCP transfer with WinSCP 4.2.5 on Windows 7 Ultimate/64 bit.

MfG, Thomas.

I am noticing a huge upload speed difference in this new version...4.25 (build 624). Mine times out on almost everything I upload. It then continues but is super slow. And the timeout message stays present even when the upload continues. I am on Cox Ultra High Speed cable internet with over 5 mb/sec upload speed.