Thanks for your post. This request has been added to tracker.

krkj wrote:

Apparently, for each file or directory selected in the preview, Winscp calls itself to do the transfer.

I forgot to mention that for this reason it is not possible to limit the transfer speed: When Winscp does the next file/folder, the speed will be back to 'unlimited'.
It would be good if limiting bandwidth were possible.

Overall Progress Bar for 'Synchronize'

This could perhaps be implemented together with a related request:
To be able to view the list of files to be synchronized/transferred while the synchronization/transfer is running and maybe even review the list of files to be synchronized/transferred.
Why?
Often I'll set up a synchronization, (de-)select files/folders to sync, start it; and then wonder why it is taking so long. The reason will be that I included files/folders that it is impractical to sync now. This is difficult to see in the progress bar window because paths are abbreviated and only the current file is shown.
If something seems wrong, then presently the only option is to abort and start from scratch.

In Commands/Synchronize.../
(at least) with the following settings:

Remote,
Mirror files,
Preview changes,

the upper Progress bar counts from 0 to 100% again and again, so that you can't see how far the total transfer has progressed.
Apparently, for each file or directory selected in the preview, Winscp calls itself to do the transfer.
It would be good to have a Grand-Total Progress bar that would reach 100% only when all is done.