[negge]

That's strange, the fact that it doesn't go any faster than 20-25 MB/s (I assume that's what you mean when you say "mo/s") without a reverse proxy means that XBMC's internal web server can't serve it faster than that. The fact that it's a bit slower with reverse proxy in use is understandable but I don't know if there is any way to fix the problem if XBMC can't send the data any faster. I have a feeling this is a Windows-specific issue since the only people who have had problems with download/streaming speeds have been Windows users as far as I can tell.

Just to rule everything out, are the files you've tried to download through XBMC Video Server located physically on the same drive that you've tried FTP/Windows file transfer from?