The configuration I was able to get for a good working Conky window with transparency is bellow. Of course I could tell you which combination doesn't work, with the why, but since there are so many of them I simply put a working one.
own_window yes # create a separate XWindow over the one from Xfdesktop own_window_type desktop # the window cannot be moved or resized own_window_hints undecorated,below,sticky,skip_taskbar,skip_pager # make it behave like it belongs to the desktop own_window_argb_visual yes # true transparency, a compositor has to be active own_window_argb_value 100 # make the background semi-transparent double_buffer yes # avoid flickering
Here is a screenshot of the desktop with Conky in the bottom right corner, I made sure there is some I/O activity going on :-)
|Xfce with Conky|