OC 10.0.3 - External Storage via WebDAV (Win7)

I want to mount my drives (8TB on Win7 x64) in Owncloud 10.0.3. It works well with SFTP. WebServer = CoreFTP
But SFTP is very slow. More than 80KB/s are not possible. But my internet is VDSL with 50 mbit down and 10 mbit upload.

Now I try to integrate the drives with WEBDAV. As a web server I use IIS (does not work) and HFS for Windows. The connection with HFS works good. But when I open the folder in OC, only one website (with folder list) is downloaded from HFS.

What am I doing wrong? Is the integration of Windows drives even possible?